Verb
see a man about a dog (third-person singular simple present sees a man about a dog, present participle seeing a man about a dog, simple past saw a man about a dog, past participle seen a man about a dog)
(idiomatic, dated) Used in place of a real explanation when excusing oneself for a short period of time, particularly (euphemistic) to use the toilet or (historical) drink alcohol.
I'll be right back, but I've got to go to see a man about a dog.