Rush, healthy plant (9)
I believe the answer is:
speedwell
'plant' is the definition.
The answer is an example.
'rush healthy' is the wordplay.
'rush' becomes 'speed' ('speed' can be a synonym of 'rush').
'healthy' becomes 'well' ('well' can be similar in meaning to 'healthy').
'speed'+'well'='SPEEDWELL'
(Other definitions for speedwell that I've seen before include "Small creeping herbaceous plant with blue or pink flowers" , "Flowering plant" , "Small blue flower of the genus veronica" , "bloomer?" , "Small plant, veronica" .)