Extreme, almost cut off (6)
I believe the answer is:
severe
'extreme' is the definition.
(synonyms)
'almost cut off' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'cut off' becomes 'severed' (synonyms).
'severed' with its final letter removed is 'SEVERE'.
(Other definitions for severe that I've seen before include "Forbidding in action or appearance" , "Formal - unsmiling" , "Harsh and punitive" , "Austere, harsh (6)" , "Extreme and difficult to endure" .)