Adjacent to a pine (5)

I believe the answer is:

along

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'adjacent to' is the definition.
I can't tell whether this definition defines the answer.

'a pine' is the wordplay.
'pine' becomes 'long' (synonyms).
'a'+'long'='ALONG'

Can you help me to learn more?

(Other definitions for along that I've seen before include "From one end to the other" , "Throughout; onward" , "Lengthwise" , "For the length of" , "Forward - in a line" .)

I've seen this clue in The Mirror.

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