Parent, merely one among many (3)
I believe the answer is:
dad
'parent' is the definition.
(dad can informally mean father)
'merely one among many' is the wordplay.
'merely one' becomes 'da' (I can't explain this - if you can you should believe this answer much more).
'among' means one lot of letters go next to another.
'many' becomes 'D' (Roman numeral for 500).
'da'+'d'='DAD'
Can you help me to learn more?
(Other definitions for dad that I've seen before include "Mum's mate" , "Popular and informal father" , "Father, in short" , "Old man" , "Pa" .)