Pieces for one not quite secure? (4)
I believe the answer is:
soli
'pieces' is the definition.
(solo is a kind of piece)
'one not quite secure?' is the wordplay.
'one not quite' means to remove the last letter.
'secure?' becomes 'solid' ('solid' can be similar in meaning to 'secure').
'solid' with its last letter taken off is 'SOLI'.
'for' is the link.
(Other definitions for soli that I've seen before include "one-man performances" , "Parts for one performer" , "individual performances" .)