See it once, moving (6)
I believe the answer is:
notice
'see' is the definition.
(thesaurus)
'it once moving' is the wordplay.
'moving' indicates an anagram.
'it'+'once'='itonce'
'itonce' anagrammed gives 'NOTICE'.
(Other definitions for notice that I've seen before include "Warning - proclamation" , "Observe - written announcement" , "Advance warning of job resignation" , "Become aware of; review" , "Formal advice - to quit?" .)