"Ho-hum” feeling (7)
'ho-hum feeling' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ennui that I've seen before include "Boredom, tedium" , "The feeling of being bored" , "having nothing to do" , "Listless feeling" , "Low interest rate" .)
(Other definitions for boredom that I've seen before include "Overseers" , "Feeling" , "Tedium, ennui" , "no interest" , "weary idleness" .)