Standard of dinner mostly OK (7)
I believe the answer is:
measure
'standard' is the definition.
(I've seen this before)
'dinner mostly ok' is the wordplay.
'dinner' becomes 'meal' (I've seen this in other clues).
'mostly' means to remove the last letter.
'ok' becomes 'sure' (both can mean 'yes').
'meal' with its final letter taken off is 'mea'.
'mea'+'sure'='MEASURE'
'of' acts as a link.
(Other definitions for measure that I've seen before include "Tape" , "Calculate size" , "Quantify" , "drink in an American bar" , "Established the size" .)