/ɪz/
[verb] The third-person singular present tense of 'to be', used to describe what something is, where it exists, or what state it is in. It connects a subject to a description, identity, or location.
'Is' is one of the oldest words in any human language, surviving almost unchanged for over 8,000 years.
The word 'is' belongs to one of the most ancient and well-travelled families in the entire history of human language. Its roots reach back to Proto-Indo-European, the reconstructed ancestor language spoken somewhere on the Eurasian steppes around 6,000 to 8,000 years ago. The Proto-Indo-European root is believed to be *h₁es-, meaning simply 'to be' or 'to exist'. This tiny syllable is one of the oldest traceable units of meaning in any language on Earth, and it has survived the fall of empires, the migration of peoples, and thousands of years of change with almost no alteration in sound.
From Proto-Indo-European *h₁es-, the word passed into Proto-Germanic as *isti, which then evolved into Old English as 'is'. Old English, spoken in Britain from roughly the 5th to the 11th century, already used 'is' in exactly the role it plays today — as the third-person singular present form of the verb 'beon', meaning 'to be'. Even in the oldest written English texts, such as Beowulf, the word appears in a form we would immediately recognise. This remarkable stability sets 'is' apart from almost every other word in English.
What makes 'is' truly extraordinary is how the same root spread across dozens of languages simultaneously. Sanskrit, the ancient language of India, has 'asti'. Ancient Greek had 'esti'. Latin had 'est', which travelled through Old French as 'est' and gave modern French its 'est' as well. Latin 'est' also produced the Spanish 'es' and the Italian 'è'. Every one of these words for 'is' in languages separated by thousands of miles descends from that same Proto-Indo-European syllable *h₁es-. The family tree is vast, yet the resemblance is unmistakable.
The verb 'to be' in English is notoriously irregular — we say 'I am', 'you are', 'he is', 'they were' — and this irregularity is itself ancient. In Old English, the verb 'beon' (to be) was already formed from three entirely separate Proto-Indo-European roots merged together over millennia. 'Is' came from *h₁es-; 'was' and 'were' came from a different root, *wes-, meaning to dwell or remain; and 'be' itself came from yet another root, *bʰuH-, related to growth and becoming. English speakers essentially stitched three ancient verbs together into one. This is called suppletion — the grammatical equivalent of building a house from parts of three different buildings.
Perhaps the most humbling thing about 'is' is what it reveals about human continuity. When a child today says 'the sky is blue', they are using a word — and a grammatical form — that a speaker of Proto-Indo-European would have recognised in outline, across eighty centuries of time. Philosophers from Aristotle to Descartes to modern linguists have argued about what 'is' truly means: does it assert existence, identity, or mere description? The word is so fundamental that questioning it becomes an act of philosophy. Even the infamous debate over President Clinton's statement 'It depends on what the meaning of the word is is' showed that this tiny two-letter word can carry extraordinary weight. 'Is' is not merely a linking word — it is the linguistic foundation of reality as we describe it.