Let's work around unknown fashion (5)
I believe the answer is:
style
'fashion' is the definition.
(I know that fashion can be written as style)
'let's work around unknown' is the wordplay.
'work' is an anagram indicator.
'around' means one lot of letters goes inside another.
'unknown' becomes 'y' (algebra).
'lets' is an anagram of 'stle'.
'stle' enclosing 'y' is 'STYLE'.
(Other definitions for style that I've seen before include "Fashion, manner, mode" , "Manner or look" , "Distinctive arrangement, elegance" , "Designate" , "way of writing" .)