Optimistic wife has one flush to play (7)
I believe the answer is:
wishful
'optimistic' is the definition.
(I've seen this before)
'wife has one flush to play' is the wordplay.
'wife' becomes 'w' (abbreviation).
'has' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'to play' is an anagram indicator.
'flush' with letters rearranged gives 'shful'.
'w'+'i'+'shful'='WISHFUL'
(Other definitions for wishful that I've seen before include "Desirous sort of thinking?" , "(Of thinking) not based on hard facts" , "Aspirant" , "This thinking is based on desire rather than fact (7)" , "Optimistic" .)