Rush to small border? (5)
I believe the answer is:
sedge
'rush' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Maybe there's a link between them I don't understand?
'small border?' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'border?' becomes 'edge' (border is a kind of edge).
's'+'edge'='SEDGE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for sedge that I've seen before include "Grass-like plant growing in wet places" , "Marsh grass" , "Marsh-dweller" , "Plant growing in swampy ground" , "water-loving vegetation" .)