Absurd sketch Rothko initially disowned (4)
I believe the answer is:
daft
'absurd' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for daft that I've seen before include "Idiotic" , "Scatty" , "'---- as a brush': dotty" , "Informally crazy as a brush" , "Half-witted" .)