Mark short notice conveyed by northeastern architectural feature (9)

I believe the answer is:
colonnade
'architectural feature' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'mark short notice conveyed by northeastern' is the wordplay.
'mark short' becomes 'colon' (colon is a kind of punctuation mark. I am not sure about the 'short' bit.).
'notice' becomes 'ad' (both can mean an advertisement).
'conveyed by' indicates putting letters inside.
'northeastern' becomes 'ne' (abbreviation for northeastern).
'ad' going inside 'ne' is 'nade'.
'colon'+'nade'='COLONNADE'
Can you help me to learn more?
(Other definitions for colonnade that I've seen before include "Row of evenly spaced pillars" , "Row of columns supporting a roof" , "supporters in a row" , "Collection of columns" , "Arcade" .)
