Learner's definition of HAPPY
a : feeling pleasure and enjoyment because of your life, situation, etc.
She was a very happy child.
I can see that you're not happy in your work. [=I can see that you do not enjoy your work]
You don't look happy. What's the problem?
We're all one big, happy family here.
I'd do anything to make/keep her happy.
She's happy playing with her toys. = She's happy when she plays with her toys.
b : showing or causing feelings of pleasure and enjoyment
I could hear the children's happy laughter in the other room.
She had a very happy childhood.
They've had a very happy marriage.
remembering happier times
a happy event/occasion
I was glad the movie had a happy ending.
c not used before a noun : pleased or glad about a particular situation, event, etc.
We are so happy that you were able to come to the party.
They are not at all happy about the rise in taxes.
He's not happy with the way the project is going.
It's great that he won the scholarship. I'm very happy for him. [=I am glad something good happened to him]
d : very willing to do something — usually followed by to + verb
I would be happy to assist you.
— used as part of a greeting or wish for someone on a special holiday or occasion
Happy birthday, Mom!
always used before a noun : lucky or fortunate
We were brought together by a series of happy accidents.
a happy coincidence
always used before a noun : fitting or suitable
a happy choice of words
He was a happy choice for chairman of the committee.http://learnersdictionary.com/definition/happy