Pill, see, could be this shape (7)
I believe the answer is:
ellipse
'this shape' is the definition.
(ellipse is a kind of shape)
'pill see could be' is the wordplay.
'could be' indicates an anagram.
'pill'+'see'='pillsee'
'pillsee' anagrammed gives 'ELLIPSE'.
(Other definitions for ellipse that I've seen before include "Inclined plane through a cone" , "Conic section" , "Shape - sell pie (anag)" , "Regular oval shape" , "Sell pie off for a geometric figure" .)