Section of Matterhorn on own? Impossible (2-2)
I believe the answer is:
no-go
'impossible' is the definition.
(I've seen this before)
'section of matterhorn on own?' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is found in the answer.
The remaining letters 'ngo' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for no-go that I've seen before include "Impossible task for goon" , "Hopeless (informal)" , "Prohibited area" , "Not possible, futile" , "Can't be done, not on" .)