Denim underwear, initially, right fit and hard-wearing (7)
I believe the answer is:
durable
'hard-wearing' is the definition.
(I've seen this before)
'denim underwear initially right fit' is the wordplay.
'initially' says to take the initial letters.
'right' becomes 'r' (common abbreviation).
'fit' becomes 'able' ('able' can be similar in meaning to 'fit'**).
The first letters of 'denim underwear' is 'du'.
'du'+'r'+'able'='DURABLE'
'and' acts as a link.
(Other definitions for durable that I've seen before include "Made to last" , "Firm" , "Capable of lasting" , "Rugged; long-lasting" , "Lasting a long time" .)