Full array one's missing in piano work (7)
I believe the answer is:
panoply
'full array' is the definition.
(I've seen this in another clue)
'one's missing in piano work' is the wordplay.
'one' becomes 'i' (Roman numeral).
'missing in' suggests deleting specific letters.
'work' becomes 'ply' (to ply a trade is to work at it).
'piano' with 'i' taken away is 'pano'.
'pano'+'ply'='PANOPLY'
(Other definitions for panoply that I've seen before include "brilliant array" , "Full array, armour" , "Impressive display" , "Trappings" , "Wide range" .)