1. have a good one - Verb
2. have a good one - Phrase
have a good one (third-person singular simple present has a good one, present participle having a good one, simple past and past participle had a good one)
(idiomatic) To enjoy an event or occasion, especially a holiday or one's birthday.
You're turning nineteen tomorrow? I hope you have a good one!
have a good one
phrase used when parting.
I've had bad jobs. Now I have a good one. I'm thankful. Maurice Greene
After my swims this weekend I think coach realized, you know what, you have to have a good one getting out of this meet. So I put the suit on and had a decent swim. Ryan Lochte