Cut in three (7)
I believe the answer is:
trisect
'cut in three' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for trisect that I've seen before include "cut into thirds" , "Cut into three pieces" , "breakaway group after sound test" , "Divide into three equal parts" , "Cut into three parts" .)