Buy tea bag outside (8)
I believe the answer is:
purchase
'buy' is the definition.
(I know that buy can be written as purchase)
'tea bag outside' is the wordplay.
'tea' becomes 'cha' (cha is a type of tea).
'bag' becomes 'purse' (synonyms).
'outside' is an insertion indicator (some letters go outside others).
'cha' going into 'purse' is 'PURCHASE'.
(Other definitions for purchase that I've seen before include "Obtain in return for payment" , "Firm grip" , "Buy something" , "become an owner" , "Procure" .)