Friend on web pages is completely different (8)
I believe the answer is:
opposite
'completely different' is the definition.
'friend on web pages' is the wordplay.
'friend' becomes 'oppo' (informal UK term for a colleague or friend).
'on' says to put letters next to each other.
'web pages' becomes 'site'.
'oppo'+'site'='OPPOSITE'
'is' is the link.
(Other definitions for opposite that I've seen before include "Totally different; facing" , "Oppose it, being faced against" , "Antithetical, vis-a-vis at" , "Corresponding" , "Contrary, antithetical" .)