pleh₁-

Root for fullness.‍​‍​‌​‍​‍​‌​‍​‌​‌​‍​‍​‌​‍​‌​‌​‌​‍​‍​‌​‌​‌​‍​‍​‌​‍​‌​‌​‌​‌​‌​‍​‍ Gives English "full", "fill", Latin plēnus, Greek plḗrēs.

Discussion

The Proto-Indo-European root *pleh₁- meant "to fill" and is one of the most productive roots in the ‍​‍​‌​‍​‍​‌​‍​‌​‌​‍​‍​‌​‍​‌​‌​‌​‍​‍​‌​‌​‌​‍​‍​‌​‍​‌​‌​‌​‌​‌​‍​‍reconstructed lexicon, generating an enormous family of words relating to fullness, abundance, and completion. The laryngeal *h₁ is reflected in the vowel length of certain derivatives and is confirmed by the comparative evidence from Anatolian and other archaic branches.

In Germanic, the initial *p became *f by Grimm's Law. Old English full descends from the zero-grade form *pl̥h₁-nó- and has remained essentially unchanged in meaning for over a thousand years. The verb fill, the adjective foul (originally "overflowing, excessive"), and folk (possibly "a multitude, a filling") may also connect to this root, though the last connection is debated.

Latin plēnus "full" is the most important reflex for English vocabulary, producing plenty, plenary, plenipotentiary, replenish, and complement (literally "that which fills up"). The Latin prefix plūs "more" (comparative of plēnus) gave English plus, plural, surplus, and nonplus. The verb complēre "to fill up completely" produced English complete, comply, and accomplish. Supply, supplement, and implement all trace back to related forms.

Greek plēthein "to be full" gave English plethora ("excessive fullness"), and polys "much, many" (from the same root) produced polygon, polyglot, polytechnic, and the prefix poly- found in hundreds of English words. Sanskrit pūrṇá- "full" confirms the Indo-Iranian reflex.

The semantic range of *pleh₁- is remarkable: from the physical fullness of a vessel through numerical abundance to abstract completion and social multitude. The root demonstrates how the Proto-Indo-European speakers extended a concrete, bodily concept — the state of being filled — into virtually every domain of thought. Few roots have been as generous in their progeny.

Notes

Source of "plenty", "plenary", "complete", "implement", "supply"