Impute (7)
I believe the answer is:
'impute' is the definition.
(I know that impute can be written as ascribe)
This is the entire clue.
(Other definitions for ascribe that I've seen before include "Attribute to, say, an old writer?" , "'Impute, assign (7)'" , "Attribute (something to a cause)" , "Attribute or impute" , "Attribute to specified source or cause" .)