Concern linked to side of Himalayan mountain (10)
I believe the answer is:
matterhorn
'himalayan mountain' is the definition.
'matterhorn' can be an answer for 'mountain' (I've seen this before). I am unsure of the 'himalayan' bit.
'concern linked to side' is the wordplay.
'concern' becomes 'matter' (both can mean an affair or happening).
'linked to' means one lot of letters go next to another.
'side' becomes 'horn' (I can't explain this - if you can you should believe this answer much more).
'matter'+'horn'='MATTERHORN'
'of' is the link.
(Other definitions for matterhorn that I've seen before include "Mountain on the Swiss-Italian border" , "Mountain in the Alps" , "peak" , "Alpine mountain" , "Alpine challenge" .)