Pretentious type of word common in Old Norse (9)
I believe the answer is:
overblown
'pretentious' is the definition.
(similar in meaning)
'type of word common in old norse' is the wordplay.
'type of word' becomes 'verb' (I've seen this before).
'common' becomes 'low' (both can mean vulgar).
'in' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'norse' becomes 'N' (abbreviation in linguistics).
'verb'+'low'='verblow'
'o'+'n'='on'
'verblow' going into 'on' is 'OVERBLOWN'.
(Other definitions for overblown that I've seen before include "roses being so past their best" , "Exaggerated" , "excessive" , "fifteen [POMPOUS]" , "pretentious" .)