Monk would have sat here quietly, Trappists ultimately needing vice, say? (5,5)

'monk would have sat here' is the definition.
(Thelonious Monk was a pianist)

'quietly trappists ultimately needing vice say?' is the wordplay.
'quietly' becomes 'piano' (synonyms).
'ultimately' suggests the final letters.
'needing' is a charade indicator (letters next to each other).
'vice say?' becomes 'tool' (vice is a type of tool).
The final letter of 'trappists' is 's'.
'piano'+'s'+'tool'='PIANO STOOL'