Utterly hot, moving about (10)
I believe the answer is:
thoroughly
'utterly' is the definition.
(thesaurus)
'hot moving about' is the wordplay.
'moving' indicates an anagram (letters are moved around).
'about' becomes 'roughly' (both can mean approximately).
'hot' with letters rearranged gives 'tho'.
'tho'+'roughly'='THOROUGHLY'
(Other definitions for thoroughly that I've seen before include "Musical with Julie Andrews" , "More than a bit" , "Really" , "Quite" , "Completely" .)