Passage — notice surmounts it (4)
I believe the answer is:
adit
'passage' is the definition.
(passage leading to a mine)
'notice surmounts it' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'surmounts' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'ad'+'i'+'t'='ADIT'
Can you help me to learn more?
(Other definitions for adit that I've seen before include "Passageway into a mine" , "Horizontal mine passage" , "Horizontal mine drainage shaft" , "Mine opening" , "Horiz. mine entrance" .)