Attain some rare achievement (5)
I believe the answer is:
reach
'attain' is the definition.
(I know that attain can be written as reach)
'some rare achievement' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'REACH' is hidden within 'rare achievement'.
(Other definitions for reach that I've seen before include "Succeed in getting to" , "Get to; extent" , "stretch of canal between locks" , "Get as far as" , "bay" .)