Round hole egg-shaped (5)
I believe the answer is:
ovoid
'egg-shaped' is the definition.
(I know that egg-shaped can be written as ovoid)
'round hole' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'hole' becomes 'void'.
'o'+'void'='OVOID'
(Other definitions for ovoid that I've seen before include "rounded shape" , "shaped like rugger ball?" , "Rounded like an egg" , "Eggy" , "like eggs!" .)