All can be preceded by ‘dark’.
Correct! Nice work.
OK, I stole this from the internet. And there are only seven words. Hope both of those shortcomings are acceptable.
Banana
Dresser
Grammar
Potato
Revive
Uneven
Assess
And it’s not the fact that all of them have at least one letter that appears more than once.
All of their lowercase parts are palindromic.
That’s actually really close.
The letters after the first letter form palindromes.
That’s basically what @pjd stated. It’s very close.
If you make them true palindromes, they become rapper names, e,g, Banana B, Potato P., Uneven U.
Bang
Bridge
Fun
King
Mad
Quit
Sing
War
They are half of well-known alliterative phrases:
Bang ??
Brooklyn Bridge
Fun ??
King Kong
Mad Max
Quiet Quit
Sing-song
War weary
Yeah, maybe not…
Half of Broadway show titles??
Fun Home
War Horse (or War Paint)
Chitty Chitty Bang Bang (still half!)
Am I getting warm?
I’m an idiot: 
Big Bang
Sorry, wrong track.
mmm
Great thought, but not correct!
They are the starts of world capital cities :
Bangkok
Bridgetown
Funafuti
Kingston
Madrid
Quito
Singapore
Warsaw
Nice job!
bowel
clasp
earth
fringe
phi
spine
spinet
suture
This list is still outstanding…
I’m pretty sure the answer you are looking for is that if you move the first letter to the back, then you have the same word written backwards. But that’s just another way of stating that everything except the first letter is a palindrome. I mean, if you have a string of letters that is a palindrome, and you have an extra letter, you can put that extra letter at either end, to make a word forwards or backwards.
Fair enough, and the correct answer!
Body parts, with the letters rearranged: elbow, scalp, heart, finger, hip, penis, instep, uterus!