Mostly unnecessary feature of record players (7)
I believe the answer is:
needles
'feature of record players' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.
'mostly unnecessary' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'unnecessary' becomes 'needless' (similar in meaning).
'needless' with its last letter taken off is 'NEEDLES'.
Can you help me to learn more?
(Other definitions for needles that I've seen before include "Western point of the Isle of Wight" , "IoW rocks" , "Slender points of a conifer" , "They may play LPs" , "nettles" .)