Round empty space - like an egg (5)
I believe the answer is:
ovoid
'like an egg' is the definition.
(oval-shaped or egg-shaped)
'round empty space' is the wordplay.
'round' becomes 'o' (o is a circular letter).
'empty space' becomes 'void' (I've seen this in another clue).
'o'+'void'='OVOID'
(Other definitions for ovoid that I've seen before include "Eggy" , "like eggs!" , "Like Humpty-Dumpty" , "Elliptical" , "rounded shape" .)