Noticed composition is deep (6)
I believe the answer is:
espied
'noticed' is the definition.
(I've seen this in another clue)
'composition is deep' is the wordplay.
'composition' indicates an anagram.
'is'+'deep'='isdeep'
'isdeep' is an anagram of 'ESPIED'.
(Other definitions for espied that I've seen before include "Saw (archaic)" , "observed in literature" , "Glimpsed" , "Caught sight of (poetic)" , "Watched" .)