There are two criteria needed in order to be a bachelor: one is that you can’t be married, and the other is that you have to be a man. Any people outside of these criteria are some other word.
The origins of bachelor are unclear, but some similar Latin words are baccalāris (“farm hand”), baccalārium (“dairy farm”), and bacca (“cow”). Maybe some bachelors spent a lot of time milking cows before getting married in the olden days. The phrase “eligible bachelor” means a guy who would make a great husband, and the phrase “confirmed bachelor” describes a man who is having so much fun being single that he’ll probably never marry. Either way, pronounce it like this: BATCH-uh-lur.