Making a stew may be a profitless activity (5)
I believe the answer is:
waste
'a profitless activity' is the definition.
'waste' can be an answer for 'activity' (waste is a kind of activity). I'm not sure about the 'a profitless' bit.
'making a stew' is the wordplay.
'making' indicates anagramming the letters.
'a'+'stew'='astew'
'astew' anagrammed gives 'WASTE'.
'may be' is the link.
Can you help me to learn more?
(Other definitions for waste that I've seen before include "Refuse - to get thin" , "Not use effectively" , "Uncultivated area" , "Barren area; rubbish" , "Misuse" .)