Friend I note investing in tea (5)
I believe the answer is:
china
'friend' is the definition.
(cockney rhyming slang, mate is china plate)
'i note investing in tea' is the wordplay.
'note' becomes 'n' (abbreviation).
'investing in' means one lot of letters goes inside another.
'tea' becomes 'cha' (cha is a type of tea).
'i'+'n'='in'
'in' going into 'cha' is 'CHINA'.
(Other definitions for china that I've seen before include "porcelain vessels?" , "Country - crockery" , "Oriental country" , "set of porcelain" , "service" .)