h₁es-tú-
“being, existence, entity”entity, essence, absent, present, interest
Abstract from *h₁es- giving Latin entia, English entity, essence, interest.
Discussion
The PIE form *h₁es-tú- (being, existence) is an abstract noun from the root *h₁es- (to be, to exist), formed with the action noun suffix *-tú-. The meaning is "the state of being" — existence conceived as a condition, a stance, a way of standing in the world. This is the root behind one of Western philosophy's most fundamental questions: what is being?
Latin esse (to be) continues the root as the most irregular and most essential verb in the language. The present participle ēns (being, entity — genitive entis) gave English entity (a being, a thing that exists). The abstract noun essentia (the quality of being, the whatness of a thing) gave English essence — a word that Cicero coined to translate Aristotle's Greek ousía (also from *h₁es-). The philosophical term existential derives from the same root through ex-sistere (to stand out, to emerge into being).
The compound forms are vast: present (prae-esse, to be before — what is before you now), absent (ab-esse, to be away — what is not here), interest (inter-esse, to be between — what lies between and therefore matters to you), represent (to make present again). Each of these common English words encodes the PIE verb for being in a prefixed form that specifies the mode of existence: being-before, being-away, being-between.
Greek eimí (εἰμί, "I am") and the participial form ṓn (ὤν, "being") continue the root. The philosophical noun ousía (being, substance, essence) — Plato's and Aristotle's central term — descends from the feminine participle. When Western philosophy asks "what is the nature of being?" it is using a PIE root to interrogate PIE semantics.
Sanskrit ásti ("he/it is") and the related sat- ("being, truth, good") continue the root in Indo-Iranian. The Sanskrit compound sat-ya (truth, from sat + ya) means literally "that which has being" — truth as the quality of existing. The religious term sattvá (being, essence, goodness) and the philosophical concept of sat-chit-ānanda (being-consciousness-bliss) in Vedantic Hinduism deploy the same root at the highest level of metaphysical abstraction.
Old English is (is), sindon (are), and the related forms continue the root natively. The English verb "to be" is suppletive — drawing on three PIE roots: *h₁es- (is, am), *bʰew- (be, been), and *wes- (was, were) — but *h₁es- provides the present-tense core. Every time an English speaker says "is," they use a word whose PIE ancestor named the most basic fact of reality: that something exists.