Altered course in spring (6)
I believe the answer is:
source
'spring' is the definition.
(thesaurus)
'altered course' is the wordplay.
'altered' indicates anagramming the letters.
'course' anagrammed gives 'SOURCE'.
'in' acts as a link.
(Other definitions for source that I've seen before include "Origin; spring" , "Place or person where something begins" , "Beginning to add" , "Origin; head of stream" , "Origin, starting-point" .)