Cutting teacher after vacation, with delight (9)
I believe the answer is:
trenchant
'cutting' is the definition.
(I've seen this before)
'teacher after vacation with delight' is the wordplay.
'after vacation' suggests removing the centre (the inside letters must vacate).
'with' is a charade indicator (letters next to each other).
'delight' becomes 'enchant' ('enchant' can be a synonym of 'delight'**).
'teacher' with its centre removed is 'tr'.
'tr'+'enchant'='TRENCHANT'
(Other definitions for trenchant that I've seen before include "Cutting, forthright" , "Incisive in style" , "Forthright, vigorous" , "Sharp" , "blunt" .)