Male beast and one female in mountainous plateau (6)
I believe the answer is:
Here is my best explanation:
'mountainous plateau' is the definition.
(I've seen this before)
'male beast and one female' is the subsidiary indication.
'male' becomes 'm' (common abbreviation).
'beast' becomes 'ass' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'one' becomes 'i' (roman numeral).
'female' becomes 'f' (abbreviation).
'in' is the link.
(Other definitions for massif that I've seen before include "mountain peak", "Geological mountain formation", "Compact mountainous area", "Mountain range", "High points", "mountain heights", "Mountainous plateau", "IMF ass found on mountainous plateau", "Highland area?" and "Compact group of mountains".)