penkʷe
“five, the number five”five, fifth
Root for the number five, yielding Latin quinque, English five, Greek pente.
Discussion
*penkʷe is the Proto-Indo-European word for "five." This numeral is notable for the dramatic phonological changes it underwent across different branches, sometimes obscuring the common origin.
In Germanic, the initial *p- was lost entirely (as Germanic had no native *p in this position under Grimm's Law, *p > f, and the cluster simplified), yielding Proto-Germanic *fimf, then Old English fīf and modern English "five." Related forms include "fifteen," "fifty," and "finger" (possibly "one of five," though this etymology is debated).
Latin quīnque shows the assimilation of the initial labial to match the labiovelar (*p...kʷ > kʷ...kʷ), a well-known dissimilatory process. From Latin come English "quintet," "quintessence," "quint," and "quintuple."
Greek πέντε (pénte) preserves the initial *p- and shows the expected delabialization of the labiovelar before *e. It yielded "pentagon," "pentathlon," "Pentecost," and the combining form penta-.
Sanskrit páñca (with palatalisation of *kʷ > c in the satem shift) gave rise to "punch" (the drink, from Hindi, originally made with five ingredients). The Avestan form is panca. Old Irish cóic and Welsh pump continue the root in Celtic with their own regular sound changes.
Notes
Pokorny 808. English five, fifth, finger, fist, pentagon, Pentecost.
Related Roots
English Words from *penkʷe
These modern English words descend from this root. Each page traces the full journey from PIE to present-day English.