Ordinary space is egg-shaped (5)
I believe the answer is:
ovoid
'egg-shaped' is the definition.
('ovoid' can be a synonym of 'egg-shaped')
'ordinary space' is the wordplay.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'space' becomes 'void' (void is a kind of space).
'o'+'void'='OVOID'
'is' acts as a link.
(Other definitions for ovoid that I've seen before include "Rounded like an egg" , "Elliptical" , "More or less egg-shaped" , "rounded shape" , "shaped like rugger ball?" .)