Raise one northern fold (8)
I believe the answer is:
increase
'raise' is the definition.
(thesaurus)
'one northern fold' is the wordplay.
'one' becomes 'i' (Roman numeral).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'fold' becomes 'crease' ('crease' can be a synonym of 'fold'**).
'i'+'n'+'crease'='INCREASE'
(Other definitions for increase that I've seen before include "Become greater in number" , "Addition, growth" , "Become bigger or greater in amount" , "Make (amount) greater" , "Make larger in a sincere way" .)