h₁en
“in, into, within”in/into
PIE preposition meaning in or into. One of the fundamental spatial roots, yielding Latin in, English "in," and Greek en.
Discussion
*h₁en is a Proto-Indo-European preposition meaning "in" or "into," one of the most fundamental and universally preserved spatial roots in the language family.
Latin in "in, into" (whence English in-, innate, internal, and the prefix in-/im-/il-/ir-) is the primary reflex. Greek en "in" (whence English en-, endogenous, energy, enthusiasm) preserves the root identically. The initial laryngeal *h₁ leaves no vowel coloring, yielding *e > i in some branches.
Old English in (modern English in, into, inn, inner, within) preserves the root directly. German in, Dutch in, and Old Norse í/inn continue the Germanic form without alteration. This is one of the few PIE roots preserved virtually unchanged across 5,000+ years.
Sanskrit ní "in, down" and Lithuanian į̃ "into" confirm the root's universality. Old Irish in "in" continues the Celtic branch.
The root's extraordinary stability across all major branches—Latin in, Greek en, Germanic in, Sanskrit ni, Lithuanian į̃—makes it one of the most secure reconstructions in comparative linguistics. Modern descendants include English in, into, inn, inner, within, and the Latin/Greek prefixes in-/en-.
Notes
Source of Latin "in", English "in", Greek "en". Fundamental locative particle.