Root drink, say, a maiden knocked back (7)
I believe the answer is:
rummage
'root' is the definition.
(thesaurus)
'drink say a maiden knocked back' is the wordplay.
'drink' becomes 'rum' (rum is a kind of drink).
'say' becomes 'eg' (both can mean 'for example').
'maiden' becomes 'm' (cricket abbreviation).
'knocked back' is a reversal indicator.
'eg'+'a'+'m'='egam'
'egam' back-to-front is 'mage'.
'rum'+'mage'='RUMMAGE'
(Other definitions for rummage that I've seen before include "Unsystematic search" , "Gear mum up to search and poke about" , "Untidy search" , "Type of sale" , "hunt" .)