Put off weightwatcher wanting the tiniest serving of ice-cream (5)

I believe the answer is:
deter
'put off' is the definition.
(both can mean to discourage)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for deter that I've seen before include "Discourage (someone from an action)" , "Discourage, put off" , "Frighten off; prevent" , "Discourage or prevent from doing something" , "'Discourage, dissuade (5)'" .)
