Mix-up in letters for settler, say? (7)
I believe the answer is:
anagram
I believe this is a double definition.
'mix-up' is the first definition.
(I've seen this before)
'letters for settler say?' is the second definition.
(letters is an anagram of settler)
'in' acts as a link.
(Other definitions for anagram that I've seen before include "new order, literally" , ""Schoolmaster" is of "the classroom", for example" , "Jumbling of letters" , "Word created from other word" , "Nag a ram (anag)" .)