Midday: arranged to dine, no? (8)
I believe the answer is:
noontide
'midday' is the definition.
('noontide' can be a synonym of 'midday')
'arranged to dine no?' is the wordplay.
'arranged' is an anagram indicator.
'to'+'dine'+'no'='todineno'
'todineno' anagrammed gives 'NOONTIDE'.
(Other definitions for noontide that I've seen before include "Time" , "lunchtime? Certainly" , "12" , "Midday" .)