Mum is one old bird full of energy joining rave (9)
I believe the answer is:
deodorant
'mum is one' is the definition.
(Mum is a brand of deodorant)
'old bird full of energy joining rave' is the wordplay.
'old bird' becomes 'dodo' (extinct bird).
'full of' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mc2).
'joining' says to put letters next to each other.
'rave' becomes 'rant' (synonyms).
'dodo' going around 'e' is 'deodo'.
'deodo'+'rant'='DEODORANT'
(Other definitions for deodorant that I've seen before include "Body odour neutraliser" , "Air-freshener" , "Smell masker" , "Substance that removes unwanted smells" , "for keeping smells away" .)