Decide to eat out - meter's running inside (9)
I believe the answer is:
determine
'decide' is the definition.
(synonyms)
'eat out meter's running inside' is the wordplay.
'eat out' becomes 'dine' (I've seen this in another clue).
'running' indicates an anagram (the letters run around to different places).
'inside' means one lot of letters goes inside another.
'meter' with letters rearranged gives 'eterm'.
'dine' enclosing 'eterm' is 'DETERMINE'.
'to' acts as a link.
(Other definitions for determine that I've seen before include "I'm entered, so find our precisely" , "Ascertain by research or calculation" , "fix" , "Come to a decision" , "Ascertain by gathering facts" .)