Six-legged creature (6)
I believe the answer is:
insect
'six-legged creature' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for insect that I've seen before include "Small air-breathing arthropod" , "Praying mantis, say" , "Possibly fly" , "Eg, beetle or fly" , "Eg, beetle or bee" .)