Happenings in flat extremely tedious (6)
I believe the answer is:
events
'happenings' is the definition.
(I've seen this before)
'flat extremely tedious' is the wordplay.
'flat' becomes 'even' (level).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'tedious' with its middle 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" .)