Release cadet, excited at start of holiday (6)
I believe the answer is:
detach
'release' is the definition.
(thesaurus)
'cadet excited at start of holiday' is the wordplay.
'excited' indicates anagramming the letters.
'at start of' indicates taking the first letters (I've seen 'at start' mean this).
The initial letter of 'holiday' is 'h'.
'cadet' with letters rearranged gives 'detac'.
'detac'+'h'='DETACH'
(Other definitions for detach that I've seen before include "Take away -- the cad (anag)" , "Separate from, remove part" , "Break off, come away" , "Disengage (something) and remove it" , "The reverse of 11 Down" .)