Look meaningfully round very fast (6)
I believe the answer is:
'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", "Eat nothing", "Suffer from food deprivation", "Deprive of food", "Die of hunger".)