I think the best way to apply keywords is to look at the card and just type what comes to your mind and keep it simple (what you have are great examples). You'd be surprised what you come up with. If you think too hard as you are trying to come up with enough keywords, you'll just forget them later. (for example, how many ways can you say "Masculine"? male, boy, man… if you don't normally say "lad", then that keyword isn't necessary).
btw, I don't know what OS you are using, but on a Mac the keywords are also included in searches so that's a plus.