Oddly, prevalent clothing for sailor? (3,6)
I believe the answer is:
pea jacket
'oddly prevalent clothing for sailor?' is the definition.
I can't tell whether this definition defines the answer.
'oddly prevalent clothing for sailor?' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
'clothing for' means one lot of letters goes inside another.
'sailor?' becomes 'jack' (informal term for a sailor).
The alternating letters of 'prevalent' are 'peaet'.
'peaet' placed around 'jack' is 'PEA-JACKET'.
(Other definitions for pea jacket that I've seen before include "sort of coat" , "Naval cover-up" .)