Move on all fours (5)
I believe the answer is:
crawl
'move on all fours' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for crawl that I've seen before include "Scramble on all fours" , "Baby-like advance" , "Progress, slow on land but fast in water" , "make slow progress" , "swarm" .)