Midday, and horse is in shape (7)
I believe the answer is:
nonagon
'shape' is the definition.
(I've seen this before)
'midday and horse is in' is the wordplay.
'midday' becomes 'noo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'and' becomes 'n' (common abbreviation for 'and').
'horse' becomes 'nag' (nag is a kind of horse).
'is in' is an insertion indicator.
'noo'+'n'='noon'
'noon' placed around 'nag' is 'NONAGON'.
Can you help me to learn more?
(Other definitions for nonagon that I've seen before include "Figure with nine, twenty-one Dn" , "Nine sided figure" , "regular figure" , "Nine-sided shape" , "Nine-sided polygon" .)