Incomplete drawing by unknown character (7)
I believe the answer is:
sketchy
'incomplete' is the definition.
(similar in meaning)
'drawing by unknown character' is the wordplay.
'drawing' becomes 'sketch' (sketch is a kind of drawing).
'by' means one lot of letters go next to another.
'unknown character' becomes 'y' (algebra).
'sketch'+'y'='SKETCHY'
(Other definitions for sketchy that I've seen before include "Not thorough or detailed" , "Imperfect" , "Vague" , "Cursory" , "lacking detail" .)