Rocky too can keep in grand shape (7)
I believe the answer is:
octagon
'shape' is the definition.
(octagon is a kind of shape)
'rocky too can keep in grand' is the wordplay.
'rocky' indicates an anagram.
'keep in' means one lot of letters goes inside another.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'too'+'can'='toocan'
'toocan' anagrammed gives 'octaon'.
'octaon' placed around 'g' is 'OCTAGON'.
(Other definitions for octagon that I've seen before include "plane figure" , "Eight-sided figure" , "Eight sided figure" , "Eight-sided object" , "regular form" .)