Look meaningfully round very fast (6)
I believe the answer is:
starve
'fast' is the definition.
(to fast is to refrain from eating food)
'look meaningfully round very' is the wordplay.
'look meaningfully' becomes 'stare' (to stare is to look at something).
'round' means one lot of letters goes inside another.
'very' becomes 'v' (abbreviation).
'stare' going around 'v' is 'STARVE'.
(Other definitions for starve that I've seen before include "Suffer from want of food" , "Deprive of food" , "Without wishing, fast" , "Suffer from lack of food" , "Fail to take in" .)