Unpunctual person disturbing a Celt more (9)
I believe the answer is:
latecomer
'unpunctual person' is the definition.
'latecomer' can be an answer for 'person' (latecomer is a kind of person). I'm not sure about the 'unpunctual' bit.
'disturbing a celt more' is the wordplay.
'disturbing' indicates anagramming the letters (I've seen this in other clues).
'a'+'celt'+'more'='aceltmore'
'aceltmore' is an anagram of 'LATECOMER'.
Can you help me to learn more?
(Other definitions for latecomer that I've seen before include "Perhaps one held up" , "One arriving after time" , "Unpunctual type o" , "Ace Merlot (anag)" , "one's a poor timekeeper" .)