Sufficient and adequate, in the end, nothing incomplete (6)
I believe the answer is:
enough
'sufficient' is the definition.
(similar in meaning)
'the end nothing incomplete' is the wordplay.
'end' says to take the final letters.
'nothing' becomes 'nought' (synonyms).
'incomplete' means to remove the last letter.
The final letter of 'the' is 'e'.
'nought' with its last letter removed is 'nough'.
'e'+'nough'='ENOUGH'
'and adequate in' 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 enough that I've seen before include "Sufficient to answer demand" , "To the required extent" , "To the required degree" , "It's said to be as good as a feast" , "As much as desired" .)