Tunnel is one of mine (7)
I believe the answer is:
synonym
This could be a double definition.
'tunnel' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'one of mine' is the second definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for synonym that I've seen before include "A word that can be interchanged with another" , "Substitute brought in for a term" , "Quick crossword clue" , "Word that can replace another in context" , "Word that can be exchanged for another" .)