Is fireman climbing on top of French mountains? (6)
I believe the answer is:
massif
'is fireman climbing on top of french mountains?' is the definition.
I can't tell whether this defines the answer.
'is fireman climbing on top of french' is the wordplay.
'fireman' becomes 'sam' (I can't justify this - if you can you should give a lot more credence to this answer).
'climbing' is a reversal indicator (in a down clue, letters climb up).
'on top of' suggests taking the first letters.
The initial letter of 'french' is 'f'.
'is'+'sam'='issam'
'issam' backwards is 'massi'.
'massi'+'f'='MASSIF'
Can you help me to learn more?
(Other definitions for massif that I've seen before include "Extensive raised area" , "Mountainous block" , "large amount of rock" , "Block of mountains" , "Geological formation of an IMF ass" .)