Happenings in flat extremely tedious (6)
I believe the answer is:
events
'happenings' is the definition.
(I've seen this in another clue)
'flat extremely tedious' is the wordplay.
'flat' becomes 'even' (level).
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'tedious' with its centre taken out is 'ts'.
'even'+'ts'='EVENTS'
'in' acts as a link.
(Other definitions for events that I've seen before include "Incidents, occasions" , "Important happenings for Steven" , "They happen at a given place and time" , "contests" , "Occurrences, happenings" .)