1. A kind salutation at meeting or parting.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• goodday,
• gooday,
• food day,
• vood day,
• bood day,
• hood day,
• yood day,
• tood day,
• giod day,
• gkod day,
• glod day,
• gpod day,
• g0od day,
• g9od day,
• goid day,
• gokd day,
• gold day,
• gopd day,
• go0d day,
• go9d day

The adjective form of "good day" is "good".

The plural form of "good day" is "good days"

The singular form of "good day" is "day"