It's placed at the end of a word (6)
I believe the answer is:
suffix
'it's placed at the end of a word' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for suffix that I've seen before include "Append" , "-ing, perhaps" , "Letter or letters added to the end to make another word" , "It's placed at the end of a word" , "-ing, for example" .)