Lines penned by old man to convey spirit of nature (5)
I believe the answer is:
dryad
'convey spirit of nature' is the definition.
I can't judge whether this defines the answer.
'lines penned by old man' is the wordplay.
'lines' becomes 'ry' (abbreviation for railway).
'penned by' means one lot of letters goes inside another.
'old man' becomes 'dad' (synonyms).
'ry' placed inside 'dad' is 'DRYAD'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for dryad that I've seen before include "Woodland deity" , "Tree nymph" , "Mythological wood nymph" , "minor divinity" , "Nymph of trees" .)