I would add the following bullet point to make this spell still do something on a failed save when you have greater than 50 hit points:

• More than 50 hit points: deafened until the end of your next turn

What about frightened instead?

The main advantage of this seems to be that it’s a bonus action to cast.

this seems like the kind of spell that would be nice to have on the bard spell list. Luckily it just so happens you get an magical secrets at 14th level, so an bard can absolutely have an vision from god and thus get the inspiration to compose a tune, a secret chord, so mighty and so infused with the song of creation that spawned the universe that it can kill people. 

Is also makes it easy to do an cheaper, earlier version of the polymorph + power word kill combo, since affected creatures are killed instantly instead of reduced to 0 hit points and so any creature under the effects of polymorph, regardless of their actual hit points, will be killed by this spell and returned to their original form as a corpse, good to keep in mind if playing an high level trickery cleric or bard

also this is an AoE banishment spell as well, neat

Quote from PalladiumTurtle >>

I would add the following bullet point to make this spell still do something on a failed save when you have greater than 50 hit points:

• More than 50 hit points: deafened until the end of your next turn

 It does already do something on a failed save if you're above 50 hit points:

Regardless of its current hit points, a celestial, an elemental, a fey, or a fiend that fails its save is forced back to its plane of origin (if it isn't there already) and can't return to your current plane for 24 hours by any means short of a wish spell.

It's just limited to celestials, elementals, fey, and fiends

That also only applies if they fail their saves... 

My party used this spell to defeat Demogorgon, they forced him to use his legendary resistance on a few powerful spells like disintegrate, but caught him off guard with divine word. Natural 1 on the saving throw.

Hp needs to be doubled on this.

Quote from Glipgin >>

Hp needs to be doubled on this.

 Because?

This is quite a wierd spell to wrap your head around mechanically; basically you only want to use it when fancing more than one enemies of the listed types, as it allows you to potentially banish several at once, or weaken those that remain (most likely the weaker chaff).

Against other enemy types you'll almost always be better off just using an area damage spell, as at these HP levels you can probably just kill weakened enemies and still deal damage to the stronger ones; the benefit of this spell against the listed types is that a 24 hour banishment is much more effective then dealing only a bit of damage, since it's "get rid of an enemy from the fight entirely" vs. "remove N% of their HP".

That said, I really wish instead of HP it was based on how badly a creature fails the roll, but the intention is probably that when faced with a big bad plus a load of chaff, the debuffs will render the chaff either harmless or easier to deal with (or even clear a bunch of them away if someone damaged them first). The other side benefit is that many of the listed enemy types have frustrating damage resistances and immunities, whereas this spell doesn't care about that, so it partially competes with weakened damage spells.

Definitely has a niche, it's just a bit weird; will probably feel great when you use it in just the right circumstances though.

Thinking about letting any players exposed to this spell and other "word" spells learn the spell (after an int check or something to keep hold of it in their mind). What do ya'll think of that?

This spell is so weak... I don't get it... a 7th level spell that only has minor negatives to creatures that are already hurt/weak. Very few creatures you're fighting when you have 7th level spells are going to be an issue if you already have it under 50 HP.

Quote from PalladiumTurtle >>

I would add the following bullet point to make this spell still do something on a failed save when you have greater than 50 hit points:

• More than 50 hit points: deafened until the end of your next turn

Quote from ConnorWalls >>

What about frightened instead?

And maybe make it deal either radiant or thunder damage.  Or possibly both.  Still, the strength of the spell seems to lie in how it banishes extraplanar creatures.  Basically an AOE version of banishment or plane shift.  Plane Shift is another 7th-level spell, but its power comes with a hefty price, a forked rod attuned to the plane you intend on traveling to.  This spell doesn't require any expensive components, can be cast using a bonus action, and has the ability to banish multiple extraplanar creatures, unlike plane shift (which can only banish one creature).  Another strength, a banished creature can't return to your plane by any means short of a wish spell.  This means not even a portal can get the banished creature back to the Material Plane, one of the fallacies of plane shift.  Generally, plane shift is more reserved for out of combat, and transporting yourself and your allies.  Divine Word is designed for large scale crowd control.      

Quote from PalladiumTurtle >>

I would add the following bullet point to make this spell still do something on a failed save when you have greater than 50 hit points:

• More than 50 hit points: deafened until the end of your next turn

The main way I can think of for using the deafened condition in combat is on a creature that might depend on hearing, such as a creature with Keen Hearing or Echolocation.  Additionally, it might make a creature struggle to detect invisible creatures, because invisible are already hidden from sight, so most creatures would rely on hearing or smell to locate them.  If a creature has Keen Hearingl, deafening them would allow your rogue to hide from them with ease.  

Eloquence Bard is ridiculous with this. Use unsettling words to debuff the save on polymorph, turn them into a slug. Then next round divine word them to oblivion.

If a target killed in this way is revivified, I believe they are still blinded, deafened, and stunned by the 30 or less effect?

Quote from Criskornelus >>

Eloquence Bard is ridiculous with this. Use unsettling words to debuff the save on polymorph, turn them into a slug. Then next round divine word them to oblivion.

 This doesn't actually function as the wording on polymorph dictates that if a polymorphed creature is reduced to zero hit points OR dies it reverts back to it's original form

I like the idea of a BBEG using this at the beginning of a campaign to kill a crowd of people in a single word. Like, imagine how scary that'd be for the party when 100 people fall to the ground and the last man standing just looks towards them.

This is one of those spells where I would be willing to have this be an action instead of a bonus action to have it be better

"Now I've heard there was a secret chord
That David played, and it pleased the Lord
But you don't really care for music, do you?
It goes like this, the fourth, the fifth
The minor fall, the major lift
The baffled king composing Hallelujah" 

If this isn't how he says it I'll be disappointed... Fits too well...