Letter from overseas somewhat inadequately sent back (3)
I believe the answer is:
tau
'letter' is the definition.
(tau is a kind of letter of the alphabet)
'somewhat inadequately sent back' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'sent back' is a reversal indicator.
'uat' is hidden within 'inadequately'.
'uat' back-to-front is 'TAU'.
'from overseas' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tau that I've seen before include "Greek letter; cross" , "Letter from Greece" , "Greek character" , "Marathon character" , "letter from foreigner" .)