Laugh raucously about moose caught climbing (6)
I believe the answer is:
cackle
'laugh raucously' is the definition.
(I've seen this before)
'about moose caught climbing' is the wordplay.
'about' becomes 'ca' (short for circa).
'moose' becomes 'elk' (synonyms).
'caught' becomes 'c' (cricket abbreviation).
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'elk'+'c'='elkc'
'elkc' in reverse letter order is 'ckle'.
'ca'+'ckle'='CACKLE'
(Other definitions for cackle that I've seen before include "Hen's squawk, witch's laugh" , "Squawk shrilly like a hen" , "See 1" , "Sound of a hen or goose" , "Laugh raucously" .)