For the spells Detect Evil and Good and Protection from Evil and Good the names of the spells are somewhat misleading. 

What would you call them instead?

I wouldn't call them Tooltip Not Found if I had to pick something... (lol)

Probably something like Detect/Protection from Plainer Energies or something like that.

There's really no good name. Detect Planar Outsiders? No, it includes undead. Detect Monsters? No, it excludes beasts and stuff. Detect The Types of Things Paladins Hate, But Not Specifically Your Paladin, More Like Every Paladin Subclass Taken As a Whole.

Something like “Detect the Unmundane” would work - it allows you to detect something that is alien to the natural order of mundane existence, be it a being from another plane or undead.  “Unmundane” is kind of a terrible word, but it does accurately capture what the spell is going for.  “Detect Alien” would also work from a strict grammatical sense, but the word “alien” carries a whole lot of baggage, making it less desirable for spell naming. 

I like @Caerwyn_Glyndwr's "Detect un-mundane" descriptor the most, even if I do have to agree with the self-admitted flaw of the word. I was thinking Detect Arcane Creature, but I'm fairly certain the spell doesn't cover the whole spectrum of whatever the arcane is in D&D.

It's a toughie, and it's a question I think about a lot but the answer is always on the tip of my tongue...

I'd make a Skyrim reference and call it "Discern the Transmundane."

Detect or protection against the unholy, or the infidel. 

Xenophobia and Greater Xenophobia?

(I kid)

 With the spells no longer focusing on alignment and instead creature type, the names are a bit off I suppose. But I honestly struggle to come up with a name that DOES perfectly describe all of those creature types and none of the creature types NOT listed. So I suppose by sheer force of inertia without a better, more elegant name in mind it's best to just keep it. 

Maybe "Detect the Supernatural" and "Protection from the Unnatural"?

There used to be a term "Outsider" that referred to any extraplanar creature, if I remember correctly.

Detect Outsider and Protect from Outsider would work.

Sense Planar (Multiversal?) Influence, so you got good, evil, law, chaos, elemental, and positive and negative charges, so to speak, on the spectrum.  Some DMs could even allow the spells to reveal travelers through the Blue Veil, spell jammers and other folks come from a different prime material world.

Something like Protection from Planar/Multiversal Power/Forces for the second spell.

Quote from Mog_Dracov >>

There used to be a term "Outsider" that referred to any extraplanar creature, if I remember correctly.

Detect Outsider and Protect from Outsider would work.

 Outsider is a creature from the outer planes. Aberrations have multiple sources (and are handled inconsistently; e.g. Protection from Evil and Good hedges them out but Magic Circle does not), Elementals are from the inner planes, Fey are from the feywild, Undead are generally from the material but powered by the Shadowfell. Detect Extra-Planar Energies would cover everything but would probably also wind up detecting most magic.

Planar would work on almost all but is undead really planar as they can be formed or found on the Prime Material

If you throw the Negative Energy Plane into your cosmology (I mean, in default 5e it's literally one half of the balanced charge of the entire cosmological structure) and go with the pretty much as canon as canon is these days in "general" D&D that necrotic and undead enervating energies originate from said Negative Energy Plane, the "planar" blanket can be applied to undead too, I think.  

Quote from MidnightPlat >>

If you throw the Negative Energy Plane into your cosmology (I mean, in default 5e it's literally one half of the balanced charge of the entire cosmological structure) and go with the pretty much as canon as canon is these days in "general" D&D that necrotic and undead enervating energies originate from said Negative Energy Plane, the "planar" blanket can be applied to undead too, I think.  

If you're going with 'energies emanate from X' that's going to pull in at least clerics, paladins, and warlocks, and quite possibly all spellcasters.

Quote from Pantagruel666 >>

Quote from MidnightPlat >>

If you throw the Negative Energy Plane into your cosmology (I mean, in default 5e it's literally one half of the balanced charge of the entire cosmological structure) and go with the pretty much as canon as canon is these days in "general" D&D that necrotic and undead enervating energies originate from said Negative Energy Plane, the "planar" blanket can be applied to undead too, I think.  

If you're going with 'energies emanate from X' that's going to pull in at least clerics, paladins, and warlocks, and quite possibly all spellcasters.

Two possibilities:

1.) It's not like an aura or a cleric channeling divine magic or a warlock exercising a rite.  Their job depends on their (non constant) contact with divinity.  Undead on the other hand, their very existence and animus is dependent on the negative (necromantic) energy giving rise to their being.  There's a significant distinction between a mortal soul that can commune with planar powers, and a way of being that is suffused with the energy of the negative plane.  In other words the commune with extraplanar powers of those PCs makes possible some of the PCs actions, but not all, so the signal ain't always a go.  Whereas undead,  the negative energy makes possible the entirety of the undead's being, so it trips the detector.

2.) I'm pretty sure Paladins were in fact subject to Detect Evil & Good in prior editions.  So, meh, bring on the retro.  But my homebrew "pact breaker" double dealer warlocks will not be subject to such mundance detections.  Rather you'll need Detect Weird but Undefined.

It would seem that undead are the ones which are the wrench in the works for a better name. My memory of previous editions was also flawed. Even though the spell was called Protection from Evil it was very effective against elementals, fiends, and fey. I suppose that being the case, the current version is close to what it was even though it has no effect on creatures of evil alignment which the old version did.

I was in a game recently in which a player (new) was insistent then disappointed that Detect Evil did not in fact detect any evil even in a room full of evil people.

They were right to feel that way. The name sucks.

Quote from Wysperra >>

It would seem that undead are the ones which are the wrench in the works for a better name.

 Abominations are a problem as well.