Scribble "sun-stroke" (6)
I believe the answer is:
scrawl
'scribble' is the definition.
(synonyms)
'sun-stroke' is the wordplay.
'sun' becomes 's'.
'stroke' becomes 'crawl' (crawl is a kind of stroke).
's'+'crawl'='SCRAWL'
(Other definitions for scrawl that I've seen before include "Write clumsily, hardly legible" , "careless writing" , "carelessly written" , "Untidy drawing" , "Write untidily" .)