Terrible smoke rising under base of apartment (6)
I believe the answer is:
tragic
'terrible' is the definition.
(I've seen this before)
'smoke rising under base of apartment' is the wordplay.
'smoke' becomes 'cigar' (smoke can mean a cigar).
'rising' says the letters should be written in reverse (going up in a down clue).
'under' means one lot of letters go next to another.
'base of' indicates one should take the final letters.
The last letter of 'apartment' is 't'.
'cigar' written backwards gives 'ragic'.
'ragic' after 't' is 'TRAGIC'.
(Other definitions for tragic that I've seen before include "Greatly distressing" , "Grievous" , "Unfortunate" , "Characterised by extreme distress or sorrow" , "heartbreaking" .)