Open tin that sufficed (6)
I believe the answer is:
candid
'open' is the definition.
(I've seen this before)
'tin that sufficed' is the wordplay.
I cannot really understand how this works, but
'tin' could be 'can' (synonyms) and 'can' is present in the answer.
'sufficed' could be 'did' ('do' can be a synonym of 'suffice') and 'did' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for candid that I've seen before include "Honest and open about what one thinks" , "Blunt; frank" , "Frank - unbiased" , "Impartial" , "Frank and outspoken" .)