Left out 'hand' in abridged dictionary (7)
I believe the answer is:
omitted
'left out' is the definition.
(to omit something is to leave it out)
'hand in abridged dictionary' is the wordplay.
'hand' becomes 'mitt' (synonyms).
'in' means one lot of letters goes inside another.
'abridged dictionary' becomes 'OED' (short for Oxford English Dictionary).
'mitt' placed into 'oed' is 'OMITTED'.
(Other definitions for omitted that I've seen before include "Hairdressing" , "Leave undone or leave out" , "Dropped" , "Left out, probably forgot" , "forgotten" .)