Learner's definition of USEFUL
[more useful; most useful]
: helping to do or achieve something
a useful invention/tool/skill
Does anyone have any useful suggestions/advice?
It can be useful to know CPR.
The Internet is useful for finding information quickly.
The therapy is useful as a treatment for diabetes. = The therapy is useful in treating diabetes.
She has become one of the team's most useful players.
Why don't you do something useful with your life?
The data could prove (to be) useful [=people may eventually find that the data is helpful] in identifying future problems.
I found this information (to be) quite useful.
Her pocketknife came in useful [=(more commonly) came in handy] when we needed to cut the tangled fishing line.
I tried to make myself useful [=to be helpful; to do something helpful] by organizing his closet for him.
the useful life of a satellite [=the amount of time during which a satellite is in good enough condition to be used]