HAPPY

• hap‧py comparative happier, superlativehappiest
• 1 having feelings of pleasure, for example because something good has happened to you or you are very satisfied with your life [≠ sad]:
• It's a lovely house and we've been very happy here.
• I've never felt happier in my life.
• He was a happy child who rarely cried.
• the happy faces of the children
• I loved her and thought I could make her happy.
• happy to do something
• John will be so happy to see you.
• happy (that)
• I'm happy that everything worked out well in the end.
• be/feel happy for somebody
• What a wonderful opportunity! I'm so happy for you.
• happy in your work/job etc
• happy to be doing something
• We're very happy to be taking part.
• the happy couple (=a couple that have just got married or will soon get married)
• 2 [usually before noun] a happy time, relationship, event etc is a good one that makes you feel happy:
• This has been the happiest day of my life.
• They had a very happy marriage.
• I have lots of happy memories of the place.
• The story has a happy ending, however.
• When's the happy event (=the birth of your child)?
• 3 [not before noun] satisfied or not worried
• happy with
• On the whole, I'm happy with the way I look.
• People living nearby are not happy with the decision.
• happy about
• Mom wasn't happy about Tess going off travelling on her own.
• I pretended to agree with her, just to keep her happy.
• happy doing something
• I'm quite happy doing what I'm doing.
• 4

   be happy to do something

  to be very willing to do something, especially to help someone:
• Our team will be happy to help.
• I'd be happy to take you in my car.
• 5

   Happy Birthday/New Year/Christmas etc

  used to wish someone happiness on a special occasion:
• Happy Birthday, Michael!
• Happy Thanksgiving, everyone!
• 6

   many happy returns

  used to wish someone happiness on theirbirthday
• 7 [only before noun] fortunate or lucky:
• By a happy coincidence, James was also in town that weekend.
• I'm in the happy position of not having to work.
• 8

   a happy medium (between something and something)

  a way of doing something that is not extreme but is somewhere between two possible choices:
• I always tried to strike a happy medium between having a home that looked like a bomb had hit it and becoming obsessively tidy.
• 9 [only before noun] formal suitable:
• His choice of words was not a very happy one.
• 10

   a/my/your etc happy place

  if you are in or go to your happy place, you imagine you are in a place that makes you feel calm and happy, because it helps you stop thinking about a bad situation
• WORD FOCUS: happy 
• cheerful behaving in a way that shows you are happy
• in a good mood happy at a particular time, and therefore friendly to other people
• pleased/glad happy because something good has happened
• delighted/thrilled/overjoyed/ecstatic very happy because something good has happened
• contented happy with your life
• optimistic/positive believing that good things will happen in the future
• gleeful/gloating smug happy because something bad has happened to someone else

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.