Road split by a grand little plant (7)
I believe the answer is:
ragweed
'plant' is the definition.
The answer is an example.
'road split by a grand little' is the wordplay.
'road' becomes 'rd' (abbreviation for road).
'split by' means one lot of letters goes inside another (some letters split a word into two).
'grand' becomes 'g' (G is short for grand as in a thousand).
'little' becomes 'wee' (similar in meaning).
'a'+'g'+'wee'='agwee'
'rd' going around 'agwee' is 'RAGWEED'.
(Other definitions for ragweed that I've seen before include "Allergenic plant" , "Plant of daisy family" , "Unwanted plant with yellow flowers" , "bloomer" , "Threat to horses" .)