1. v. To orgasm
2. v. To masturbate
3. v. To eject semen, whether on one's own or with assistance
Note: The term is not necessarily aimed for men, women can "achieve" as well, and I'm sure we all want to see that. You just replace any synonym of orgasm with the word "achieve" in all of it's tenses to use in normal conversation.
1. My roommate was out so I had plenty of time to achieve.
2. I was bored so I spent the day achieving.
3. I achieved inside a girl last night, then she fell asleep so I achieved some more on my own.