Wearing suit, to a large extent (2,6)
I believe the answer is:
in spades
'to a large extent' is the definition.
(as in having something in spades)
'wearing suit' is the wordplay.
'wearing' becomes 'in' (as in being 'in' certain clothes).
'suit' becomes 'spades' (playing card suit).
'in'+'spades'='IN SPADES'
(Other definitions for in spades that I've seen before include "To have lots of it" , "Decidedly" , "To a very great degree" , "Very much so" , "by the yard" .)