1. cause to feel happier or more cheerful
let's try and cheer them up
To be 'in good cheer' is a dated expression meaning to be happy and in good spirits. To 'cheer someone up' is the act of making them feel more cheerful or happy. This is used very often in social situations to encourage someone not to be sad about something "Cheer up, it's not as bad as it seems". Similar to the expression 'chin up'.