Spheroid (5)
I believe the answer is:
round
'spheroid' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for round that I've seen before include "Description of Tweedledum" , "with 6D [SPARE TYRE]" , "Circular - 18 holes" , "(Of voice) rich, mellow" , "unsuitable for square pegs" .)