In searching out information about befriend as a verb, I came across a word I hadn't heard before - it's privative. I came across the word in the summary of an article about be- and bi- used as prefixes in verbs of deception, like beguile and betray. There's another word, bewray, meaning to divulge, reveal or betray, but that word's not used nowadays at all.
I think the article argues that this psychological sense of the prefix came about via an earlier privative construction, such as in bereave or behead.
A prefix can be privative. Hmm... What does that mean? I was beginning to feel completely lost, until I looked up the meaning of this new word. Privative, according to thefreedictionary, means 'altering the meaning of a term from positive to negative'. Yeah... getting beheaded would be a very negative experience.
And then, of course, there's privation, which sounds similar, so I'm going to remember this new word, privative, by comparison with privation and being deprived of something.
Well, I'll remember it for as long as I can - probably till tomorrow morning if I'm lucky.