1. n. (one’s) father. What time does your old man get home?
2. n. (one’s) husband. My old man is sick and can’t come with me.
3. n. (one’s) boyfriend. I got my old man to take me to see that movie I told you about.
4. and the old man n. the boss; a high-ranking officer. (Always with the in this sense.) The old man says do it, so you had better do it.