Get on a bit, doddery (6)
I believe the answer is:
obtain
'get' is the definition.
('obtain' can be a synonym of 'get')
'on a bit doddery' is the wordplay.
'doddery' indicates anagramming the letters.
'on'+'a'+'bit'='onabit'
'onabit' with letters rearranged gives 'OBTAIN'.
(Other definitions for obtain that I've seen before include "Get, procure" , "Get or lay hold of" , "Come into possession of" , "Take possession of" , "Get or receive" .)