Plant needing a support, post to keep it in place (5-4)
I believe the answer is:
mares-tail
'plant' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
'a support post to keep it in place' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'support' could be 'rest' (e.g. a shoulder rest is a support for shoulder) and 'rest' is located in the answer.
'post' could be 'mail' (synonyms) and 'mail' is located in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'needing' is the link.
Can you help me to learn more?
(Other definitions for mares-tail that I've seen before include "Long streak of cirrus cloud" , "Common water plant" .)