Pervasive plant ever spreading (9)
I believe the answer is:
prevalent
'pervasive' is the definition.
(thesaurus)
'plant ever spreading' is the wordplay.
'spreading' indicates anagramming the letters.
'plant'+'ever'='plantever'
'plantever' anagrammed gives 'PREVALENT'.
(Other definitions for prevalent that I've seen before include "Widely accepted" , "general" , "Ruling" , "Widespread - current" , "powerful" .)