Simplified form of 歡. Phonosemantic compound. 欠 represents the meaning and 雚 represents the sound. 欠 (yawn) is a pictograph of a person with an open mouth, used here to represent a person joyfully laughing.

Evolution

Seal script

Shuowen (~100 AD)

Clerical script

Eastern Han dynasty (25-220 AD)

Clerical script

Eastern Han dynasty (25-220 AD)

Traditional script

Modern

Simplified script

Modern