 It's back-to-school time, so today, in surprisingly connected etymologies, we're going to school you in some educational etymologies. Okay, parents, time to start thinking of your children's back-to-school apparel. The word parent comes from the Latin verb parara to bring forth produce, ultimately from Proto-Indo-European para with the same basic meaning. This root also leads to the Latin verb parare to prepare. Also the source of the word prepare literally produce in advance, which, when combined with the prefix add to, gives us apparel, which originally referred to fighting apparatus, another related word, such as armor and weapons, unless it comes from vulgar Latin ad particulare to put things together. Have you ever had a severe teacher at school? Well, that's probably etymologically appropriate, if not pedagogically. School comes from Greek schole, meaning leisure, as well as school, from the idea that you need leisure time away from working to be able to be educated. But literally, schole means a holding back, and thus a rest, coming from Proto-Indo-European seg to hold. This root probably also leads to Latin severus stern, from the derived form seguer, toughness, steadfastness, giving us English severe. Does your math teacher ever do calculations on the blackboard with chalk? Well, etymologically, that would be appropriate. Calculate comes from Latin calculus, reckoning account, which had the original sense of a pebble used as a reckoning counter, and is a diminutive of calcs, limestone. This Latin word calcs was barred into West Germanic, becoming chowk in Old English, and then chalk in Modern English, referring more specifically to the particular type of limestone commonly found in Britain. Any English student can tell you that a text can be subtle and hard to understand. Latin textus meant literally woven thing, but could metaphorically be used to refer to the style or texture of a work, and eventually the written work itself. The Latin subtilis meant finely woven, from sub, under, plus tele, web. Both text and subtle can thus be traced back to the Proto-Indo-European root, tex, meaning to weave. If you're like me, you're deliriously happy to learn a new etymology, as you should be. Delirium comes from Latin delirium madness and deliriare, to be crazy, rave, literally to go off the furrow, a plowing metaphor from the phrase De Lira, off the furrow. Latin lira comes from Proto-Indo-European lace, track, furrow, which came into the Germanic branch, eventually giving us English learn, this time from the metaphor of gaining experience by following a track. Thanks for watching. This is one in a series of occasional short videos about connected etymologies. To see more, you can follow the endless knot on Twitter, Facebook, or Instagram.