Egg-shaped or round hole (5)
I believe the answer is:
ovoid
'egg-shaped' is the definition.
('ovoid' can be a synonym of 'egg-shaped')
'round hole' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'hole' becomes 'void'.
'o'+'void'='OVOID'
'or' is the link.
(Other definitions for ovoid that I've seen before include "rounded shape" , "egg, say" , "shaped like distorted circle" , "shaped like rugger ball?" , "More or less egg-shaped" .)