Zero change in location of eggs (5)
I believe the answer is:
ovary
'location of eggs' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'zero change' is the wordplay.
'zero' becomes 'O' (O resembles 0).
'change' becomes 'vary' (synonyms).
'o'+'vary'='OVARY'
'in' is the link.
Can you help me to learn more?
(Other definitions for ovary that I've seen before include "Female organ in which eggs are produced" , "Egg producing organ" , "Egg-producing gland" , "egg supplier" , "(Human) egg producer" .)