peh₂-s-
“to feed, to graze, to protect”graze
Root for feeding and grazing animals. Gives Latin pāscere "to feed", English "pasture", "pastor".
Discussion
The root *peh₂-s- ("to feed, to graze, to protect") is an extended form of *peh₂- ("to feed"), treated in LIV² (s.v. *peh₂-) and Pokorny (IEW 787). The laryngeal *h₂ produces the characteristic a-colouring seen in Latin and other reflexes. The semantic development from "feeding" to "protecting" (the one who feeds the flock is the one who guards it) is ancient and productive.
Latin pāscere ("to feed, to graze") and pābulum ("food, fodder") continue the root directly, with *peh₂- > pā- by regular laryngeal vocalization. The noun pāstor ("shepherd, one who feeds") yields English pastor, pastoral, and pasture. The compound re-pāscere gives repast. The verb pābulārī ("to forage") contributed to English foraging vocabulary.
The o-grade *poh₂-s- likely underlies Latin pānis ("bread"), whence English pantry, companion (com-pānis, "one who shares bread"), and company. This etymology, while widely accepted, is not universally agreed upon.
Greek patéomai (πατέομαι, "I eat, I feed on") preserves the root, and the noun páthnē ("manger, feeding-trough") shows the concrete sense.
In Germanic, Old English fōda ("food") and fēdan ("to feed") derive from *peh₂-t- or a related extension, with Grimm's Law giving *p > f. Modern English food, feed, fodder, and foster all belong to this root family. The semantic extension to foster ("to nourish, to rear") parallels the Latin pastor development exactly.
Sanskrit pā́ti ("protects, guards") shows the semantic shift from feeding to protecting already completed in Indo-Iranian. The connection between nourishment and protection is thus reconstructable to PIE itself.
Notes
Also source of "food", "foster", "fodder" via *peh₂-