Greek trokhiskos, diminutive of trokhos, wheel, from trekhein, to run, passed through Late Latin trochiscus and Old French trocisse into English troche, attested from the 1590s: a small, strictly circular, tablet of medicinal paste dried hard and dissolved slowly in the mouth. The word's cousins run everywhere: the trochee, the running metrical foot, the trochanter of the femur, the truck and the trouser-press's wheel. RxList's definition is the archive's favorite kind of pedantry: strictly speaking, a troche should be circular, the shape carrying the etymology like a signature.
The shape was the technology: a wheel rolls, a round lozenge rotates in the mouth, dissolving evenly, the form engineered for the slow release the word promised. The diamond-shaped lozenge, the word from heraldry's losenge, is the wheel's rival, the shape that does not roll, and the two words still divide the cough-drop aisle by geometry, the round ones heirs of the Greek runners, the diamond ones heirs of the French jewel. The pharmacy kept both, and the aisle is a frozen etymological dispute you can buy by the bag.
The claim: the troche's wheel is the archive's smallest perpetual-motion exhibit, the running root, trekhein, embedded in a medicine whose entire function is to keep moving until gone, the dose as a wheel that dissolves itself, and the modern timed-release capsule the same runner wearing plastic, release profiles being just controlled rolling. Verdict: the mechanism reading is the archive's, the root is the dictionary's. The Greek pharmacists named the pill for motion, and four hundred years of pill coatings later, the industry still sells controlled motion. The wheel runs. The patient pays by the lap.
If the medicine was named for a wheel, what was it meant to set in motion?