The instruction to be economical is falling on deaf ears (7)
I believe the answer is:
useless
'deaf ears' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I can't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for useless that I've seen before include "Counterproductive" , "Of no practical application, not worth keeping" , "idle" , "Worth zilch" , "Far from impressive" .)