Pair involved in most woe (7)
I believe the answer is:
twosome
'pair' is the definition.
(I know that twosome is a type of pair)
'involved in most woe' is the wordplay.
'involved in' indicates an anagram (involved can mean complex or confusing).
'most'+'woe'='mostwoe'
'mostwoe' anagrammed gives 'TWOSOME'.
(Other definitions for twosome that I've seen before include "match" , "Couple" , "game of golf" , "Item" , "Pair, duo" .)