Wader, small, too quiet in breakwater (9)
I believe the answer is:
sandpiper
'wader' is the definition.
(sandpiper is a kind of wader)
'small too quiet in breakwater' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'too' becomes 'and' (I've seen this in another clue).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'in' means one lot of letters goes inside another.
'breakwater' becomes 'pier' (I've seen this before).
'p' put inside 'pier' is 'piper'.
's'+'and'+'piper'='SANDPIPER'
(Other definitions for sandpiper that I've seen before include "knot" , "Shore bird" , "Ground-dwelling wading bird" , "Stint" , "Coastal wading bird" .)