Not hard to damage sleeve (3)
I believe the answer is:
arm
'sleeve' is the definition.
(synonyms)
'not hard to damage' is the wordplay.
'not' is a deletion indicator.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to damage' becomes 'harm' (synonyms).
'harm' with 'h' taken out is 'ARM'.
(Other definitions for arm that I've seen before include "Supply weapons" , "Activate warhead" , "Activate fuse" , "Body part" , "Maybe rifle" .)