Unusual for one to playact and mess about (8)
I believe the answer is:
atypical
'unusual' is the definition.
(similar in meaning)
'one to playact and mess about' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
an anagram of 'playact' is 'atypcal' which is located in the left over letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for atypical that I've seen before include "Not representative or usual" , "out of character" , "Not characteristic" , "Not conforming to a type" , "Unrepresentative" .)