More spesific how? It though they just said "action" when they refer to your "standard" action, because that's what it's called.
The spell stinking cloud has been confirmed to work this way. You waste your action, but still keep your bonus action and reaction etc.

Curse a creature that every time it drinks a liquid it takes 1d4 acid damage. 

For you posters worried about the touch range of this spell, maybe have a look at the 1st-level spell "Find Familiar."

"Finally, when you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell. Your familiar must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it."

For those of you who can't see the value of giving disadvantage on saves, maybe consider "Flesh to Stone," "Feeblemind" or a hundred other spells.

If you're worried about landing this in the first place, do yourself a favor and read the 2nd-level ability of the Divination Wizard: 

"Portent

Starting at 2nd level when you choose this school, glimpses of the future begin to press in on your awareness. When you finish a long rest, roll two d20s and record the numbers rolled. You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

Each foretelling roll can be used only once. When you finish a long rest, you lose any unused foretelling rolls."

***

Spells work together. Are you guys wizards or are you orcs? There's more to this than "MEEE PRESS KILL BUTTON KILL KILL."

I've run not only successful but absolutely terrifying wizards who nonetheless use exactly zero spells that cause damage. Spells like Bestow Curse are essential to that success. Turning a powerful enemy to stone and then teleporting him into your garden is both defeating that enemy and making him or her your prisoner, which can be very useful.

But, by all means, be a boring murder-hobo and take fireball instead.

I suggest adjusting the times and clearer rules for what can be don't. First make the times how often they can make a saving throw to break a curse above 5th level and when its 8th level and above make it  that they need a remove curse to try to save. Also make the times more flexible by splitting the every two levels into every level level 6 = 24 hours, level 7= 1 week, level 8= month and 9 =  year. Finally open up the effect more by  letting it replicate the effects of any second level spell or lower at the dm's discretion.  This lets npcs curse shop keepers to never be able to lie to them and things like that but more importantly lets them try it at a reasonable level range like 7th level spells instead of the distant dream of 9th level spells. 

if you use the third effect  "While cursed, the target must make a Wisdom saving throw at the start of each of its turns. If it fails, it wastes its action that turn doing nothing." Does the enemy get reactions or oppurtunity attacks? Would they make a roll to break the curse for it?

Looking for input. It says you can make up your own effect (within reason) so how does reducing the targets speed to half compare? I thought it could be interesting.

Quote from doomsdaydesign >>

Because it's granted by a 5th level eldritch invocation, 1/day, called Sign of Ill Omen

 

 

 Another point, warlocks get hex, which is basically a lower-level version of bestow curse.  

They waste their action, but can still use their bonus action, reaction, movement etc. They only lose their action, not their whole turn, as some people think.
And no, they dont break the curse if they succeed on that save. Like with every other effect, the curse is only removed if concentration is lost, the duration runs out, or if removed by something like remove curse.

This is... truly powerful...

Wait for the clerics is it only death domain? Or can all clerics use it?

you manage to touch the bbeg and cast this he runs you chase you don't want it wearing off

Quote from Kittycatscratch >>

Wait for the clerics is it only death domain? Or can all clerics use it?

 It's all clerics. What made you believe only death domain?

alright, so this spell sounds really cool, and it is admittedly pretty good in combat in some scenarios. However, you must remember that this is a 3rd level spell, and the classes this is available for don't exactly have that many 3rd level spell slots. Now, if you're facing one enemy, and you really don't want them to be good at one particular thing, you can do that, but any more than one powerful enemy and this spell is just wasted. It's good at synergy with other damage dealing/debuff spells, to an extent, but once again, it only works on one person, so unless that's the only person you need to deal with, then this spell is only as useful as the person is a threat to you with that particular stat. I mean, if you really want to have a powerful debuff that works on multiple people at a time or works on basically everybody, pick Heat Metal, Color Spray, Chromatic Orb, Bane, Blindness/deafness, or like, anything that does basically this at equal to or lower level. Overall, it's occasionally pretty good, but at literally any other time you're just wasting a spell slot casting it, because aside from that one person everybody else is unaffected by that 3rd level spell. This is as opposed to Bane, Color Spray, Pyrotechnics, or even Protection from Evil and Good. To put it differently, there are better spells than this one, and this one is only as good as the opponent you target is threatening with that specific stat.

How the crap is this not a warlock spell?

Does this also mean that if something has a negative modifier to wisdom you could stun lock it?

For maximum social mischief, here are 100 fey pranks that can be reskinned into curses: https://www.reddit.com/r/d100/comments/8hxmlj/lets_build_fey_pranks/

Why this isn't on the warlock spell list, and the aberrant mind sorcerer spell list is befuddling to me. 

10th level Valor/Swords Bard

Get Swift Quiver through Magical Secrets.

Cast Swift Quiver. 
Next turn, cast this spell at 5th level so it doesn’t require Concentration. Choose “your attacks and spells deal 1d8 extra necrotic damage to the target.” Then Attack twice with Swift Quiver as a Bonus Action. 
On all turns after this, you can attack at total of 4 times, with each attack doing 1d8 extra damage. With a Longbow and 20 DEX, this equals 8d8+20 damage, or an average of 56 DPR if all shots hit.

Warlocks can get it through an invocation. This has already been said multiple times in the comments.