Let’s get right into it, shall we?
Learn comes from the Old English leornian, which just means to learn so there weren’t any big jumps here. Although amusingly enough there was a word leorningcild, which means student, and is literally “learning child”. Anyway, leornian comes from the Proto Germanic lisnojanan, which actually had a sense of meaning that was “to follow or find the track”. I mean, you can see how learning is following a path? It’s actually from the Proto Indo European lois-, furrow or track. It makes sense (kind of), but still, wow.
Teach comes from the Old English taecan, which could mean teach or show, or even translate. The past tense of the word, much like our own version, switches from a c to a t. Which of course is because that’s where taught comes from. Taught came to us from the Old English tahte. No explanation why the letter switch, but let’s just chalk it up to Old English being Old English. Anyway, taecan comes from the Proto Germanic taikijan, to show, and the Proto Indo European root deik-, which has so many related words that it would take a long time to get through them. Maybe the next time I’m in the mood for doing a long series.
The origins of educate aren’t from Old English, so maybe it’ll actually make sense. It showed up in the mid fifteenth century from the classical Latin educatus, educated, and its verb form educare, which means teach or train. It’s actually related to another verb, educere, to lead, a mix of the prefix ex-, out, and ducere, also to lead. That word can be traced to the Proto Indo European deuk-, which means to lead and I’m sure has shown up in one of my etymology posts at some point.
Finally today, we’re looking at know. It comes from the Old English cnawan, which basically means know and yes, would have been pronounced with the hard C sound. It’s from the Proto Germanic knew and Proto Indo European gno-, to know, so this word stayed pretty steady through the years. Until we lost the K sound in front of it. Why’d we ever do that?
Tony Jebson’s page on the Origins of Old English