This makes trestle from mixture of letters (7)
I believe the answer is:
anagram
'this makes trestle from mixture of letters' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
Can you help me to learn more?
(Other definitions for anagram that I've seen before include "Rearrangement of a word's letters to form new word(s)" , "Word that rearranges another's letters" , "Word(s) rearranged to form others" , "Word play" , "a mix of characters" .)