Midday, getting horse into shape (7)
I believe the answer is:
nonagon
'shape' is the definition.
(I've seen this before)
'midday getting horse' is the wordplay.
'midday' becomes 'noon' (synonyms).
'getting' indicates putting letters inside.
'horse' becomes 'nag' (term for an old horse).
'noon' placed around 'nag' is 'NONAGON'.
'into' is the link.
(Other definitions for nonagon that I've seen before include "regular figure" , "Figure with nine, twenty-one Dn" , "geometric figure" , "Figure with nine sides" , "Nine-sided polygon" .)