Check lizard (7)
I believe the answer is:
monitor
I believe this is a double definition.
'check' is the first definition.
(synonyms)
'lizard' is the second definition.
(I know that monitor is a type of lizard)
(Other definitions for monitor that I've seen before include "Supervisor - lizard" , "one checks continuously" , "Large lizard; TV screen" , "Keep tabs on; lizard" , "Keep a watching brief" .)