In Romance languages, the history of the word “to know” is pretty straightforward. Yeah, it comes from Latin. Yawn.
Galician/Portuguese conhecer, Spanish conocer, Italian conoscere, French conaître, Catalan conèixer… they all stem from Latin cognoscere, the present of cognosco, where gnosco was already “to be acquainted with”, which was derived from PIE *ǵneh₃- meaning just that. Fascinating, I guess.
From that root, through Proto-Germanic *knēaną (“recognize”, “understand”), we got English know. Oh the excitement.
But wait! Don’t leave yet!
You’d assume per the previous paragraph that other Germanic languages have a similar story to tell. Nothing of the sort!
Dutch weten, German wissen and Swedish veta, to name a few, come from another Proto-Germanic word, *witaną, exactly “know”. You might recognize that root in English words like wit or wisdom.
And this is the final reveal: *witaną is the perfect form of the verb “to see”, i.e., it literally means “I have seen”! It’s a dual feature also present in its Greek cognate εἴδω – both of them descend from the Proto-Indo-European root *weyd- “to see” that also gave us video and vision through Latin.
To see is to know. Guaranteed since ancient times!
Sources: this Reddit comment gave me the lead and I also consulted some Wiktionary articles      
Originally published in The blind mouse.