(s)tew-
“to push, to strike”push, strike, beat
Root for pushing/striking, yielding Latin tundere (to beat), English stun, stutter.
Discussion
The PIE root *(s)tew- (to push, to strike, to knock — with the s-mobile in initial position) produced vocabulary for both physical impact and the things produced by impact. The parenthetical s- indicates that the root appeared in two forms in PIE — *stew- and *tew- — with both preserved in the daughter languages.
Latin studēre (to be eager, to apply oneself — originally "to push toward," to exert effort in a direction) gave English: study (the act of pushing oneself toward knowledge), student (one who pushes/strives), studio (a place for studying/working), and studious. The semantic development from "push/strike" to "be eager" to "study" passes through the concept of directed effort: to study is to push your mind at a problem.
Latin tundere (to beat, to strike repeatedly — from the variant without s-mobile) gave: contusion (a bruise — the result of being struck), obtuse (beaten blunt — then metaphorically dull-witted), and the combining form -tund- in medical terminology.
English stew (OE stūfian, "to heat in steam" — possibly from this root through the image of pushing/agitating in hot liquid) may be connected, though the derivation is debated. German stoßen (to push, to strike) continues the root transparently.
Sanskrit tudáti ("he pushes, he strikes") continues the Indo-Iranian reflex without the s-mobile.
The root's semantic arc from physical striking to intellectual striving is one of the most culturally productive in the PIE vocabulary: the student is, etymologically, a striker — one who beats at the doors of knowledge. The university studio and the boxing ring share the same PIE root.
Notes
Pokorny 1032-1034. English contusion, obtuse.