Styluses unnecessary, mostly (7)
I believe the answer is:
needles
'styluses' is the definition.
(needle is a kind of stylus)
'unnecessary mostly' is the wordplay.
'unnecessary' becomes 'needless' (similar in meaning).
'mostly' means to remove the last letter.
'needless' with its last letter taken away is 'NEEDLES'.
(Other definitions for needles that I've seen before include "Sewing aids" , "Feature of Christmas trees" , "passes through" , "Annoys the pointed implements?" , "Isle of Wight chalk monoliths" .)