Quiet little chap, this crony? (3)
I believe the answer is:
pal
'crony?' is the definition.
('pal' can be a synonym of 'crony')
'quiet little chap' is the wordplay.
'quiet' becomes 'pp' (musical abbreviation for pianissimo).
'little' means to remove the last letter (the word is not quite complete).
'chap' becomes 'al' (man's name).
'pp' with its last letter taken off is 'p'.
'p'+'al'='PAL'
'this' acts as a link.
(Other definitions for pal that I've seen before include "Close friend" , "Mate, buddy" , "Friend (colloq.)" , "Bud" , "Buddy, chum" .)