changing words

I found this book at work. It's a compiled collection of Robert Heinlein's letters, edited by his wife, and published under the name he requested: Grumbles From Beyond The Grave. I was browsing through it and found some uses of a couple words which made me wonder at how quickly our language changes.

For example, most people know that the term 'gay', when used to mean 'homosexual', is a fairly recent development. And it seems fairly common for people to know that 'gay' meant, roughly, 'happy'. Well, when I was reading this Heinlein book, he was using 'gay' in contrast with 'happy', and I'd never seen that before. The best I can tell, he was using 'happy' to mean more of a long term state, like maybe, "I'm happy with my life", while 'gay' is something more immediate, like the feeling you would get after a fun dance. I'd never realized that distinction before.

He used another word in a way I'd not noticed before. Rather, with more subtlety to the meaning than I'd realized. As far as I've known, striving for something just means working hard to get it. But, and I've noticed this in other sources, too, Heinlein seems to be using it in a way that puts it in a negative light. Like with striving one is putting too much energy into reaching that goal. There's a definite negative connotation.