Yearns to have house on or very close to sea (9)
I believe the answer is:
Here is my best explanation:
'very close to sea' is the definition.
I can't judge whether this definition defines the answer.
'yearns to have house on' is the wordplay.
'yearns' becomes 'longs' ('long' can be a synonym of 'yearn').
'to have' says to put letters next to each other.
'house' becomes 'ho' (abbreviation for house).
'on' becomes 're' ('on' can be mean 'with reference to'**).
'or' acts as a link.
(Other definitions for longshore that I've seen before include "Relating to the land bordering the sea" and "very close to the sea".)