Causes to yawn (5)
I believe the answer is:
bores
'causes to yawn' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bores that I've seen before include "Dull tedious talkers" , "Drills or wearies" , "Makes a hole with a pointed tool" , "Tedious people or drills" .)