Close pit to break one million northern lefties, essentially (8)
I believe the answer is:
imminent
'close' is the definition.
(similar in meaning)
'pit to break one million northern lefties essentially' is the wordplay.
'pit' becomes 'mine' (mining pit).
'to break' is an insertion indicator (inserted letters break the word apart).
'one million' becomes 'im' (resembles mm).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'essentially' says to take the centre.
The middle letter of 'lefties' is 't'.
'im'+'n'='imn'
'mine' placed into 'imn' is 'imminen'.
'imminen'+'t'='IMMINENT'
(Other definitions for imminent that I've seen before include "Likely to occur at any moment" , "Looming or impending" , "Happening any moment now" , "Liable to occur soon" , "now expected" .)