Regretted a sort of bad omen about earth (8)
I believe the answer is:
bemoaned
'regretted' is the definition.
('bemoan' can be a synonym of 'regret')
'a sort of bad omen about earth' is the wordplay.
'a sort of' indicates anagramming the letters.
'about' is an insertion indicator.
'earth' becomes 'E'.
'bad'+'omen'='badomen'
'badomen' with letters rearranged gives 'bmoaned'.
'bmoaned' placed around 'e' is 'BEMOANED'.
(Other definitions for bemoaned that I've seen before include "Lamented, deplored" , "regretted" , "Complained of, lamented" .)