What the word covers now
In current English, entire is the everyday adjective for something taken as a whole: a book read from first page to last, a day spent in one place, a building whose roof is still on. It sits near complete and total, yet it often keeps a quieter note of intactness, of nothing having been cut away. That note is clearer in the specialist uses. Botanists call a leaf entire when its margin is smooth, without teeth or lobes. Stockmen call a male animal entire when it has not been castrated. Those senses look like jargon until the older meaning is restored. The origin of the word entire is, at root, a claim that something has not been touched.
A French loan, not a native heir
English did not inherit the word from Old English. It borrowed it in the Middle English period, around the mid-fourteenth century, when French still supplied a large share of adjectives for description, law, and status. The immediate source is Old French entier, also recorded in Anglo-Norman, with the sense whole, unbroken, intact. Middle English spellings include entere and enter. A later form intire, now obsolete, shows that writers were still deciding how to represent the first syllable.
Standard dictionaries trace the French word to Latin integrum, a form of integer. Some accounts treat integrum as the accusative, others as the neuter; Romance languages commonly continued a non-nominative case, so the disagreement is about which Latin shape French inherited, not about the ancestor itself. What English received was already a French word, not a raw Latin stem.
The same path is visible across the Romance family. French still uses entier for whole. Spanish entero, Italian intero, Portuguese inteiro, and Romanian întreg are close relatives. English entire belongs with that group, not with native Germanic pairs such as whole or all.
The Latin pieces: not plus touch
Latin integer meant intact, complete, uninjured. Used of people and character it could mean untainted or upright. Its parts are the negative prefix in- and the same verbal root that appears in tangere, to touch. The literal picture is something nobody has laid a hand on: undamaged, uncut, with nothing removed.
That analysis is the usual one in modern etymology. Italic reconstruction gives a form *n̥tagros with the same sense of untouched. Indo-European handbooks often connect the Latin further to a root written *tag- or *teh₂g-, meaning to touch or handle. The notation of that deeper root is not settled in every source; what matters for English is the Latin compound, not a quarrel over the asterisked ancestor.
French sound change hid the morphology. Once the g of integer had been absorbed, entire no longer looks like in- plus touch. The family only becomes visible when the French loan is set beside later, more Latinate relatives that English took in by a different route.
How the senses moved
The first English uses, of things, meant whole and intact. That physical sense never left. The botanical term for a smooth leaf margin is the same idea applied to a plant organ that has not been notched. The zoological sense, of a stallion or other male left uncastrated, is likewise about a body not cut. In both fields, entire still means unaltered at the edge.
A moral and emotional range grew beside the physical one. Early modern writers could call a person entire to a cause, meaning undivided in loyalty, or speak of entire fear as unmixed. Dictionaries still list an archaic sense of unalloyed or homogeneous. Those uses have largely faded from ordinary speech, leaving the blunter modern meaning: the whole of something, with no part left out.
As a noun, entire is now rare for the whole of a thing; entirety and the phrase the entire X took over that work. In specialist English the noun survives for an uncastrated horse, for a fully marked postal cover in philately, and, historically, for beer drawn complete from the brewery rather than blended in the tap. In mathematics an entire function is one holomorphic on the whole complex plane: again, no region left out.
Two doors from the same Latin word
English later borrowed integer itself, first as an adjective in the Latin sense of whole around 1500, then as the mathematical noun for a whole number in the 1570s. Integrity, integral, and integrate arrived through the same Latin family, stressing moral soundness, being essential to a whole, or making something whole again. Tact, tangible, and tangent come from tangere without the negative prefix.
The useful split is the path, not a change of idea. Entire is the French-shaped descendant of Latin integer. Integer is a later scholarly import of the same Latin word. One became the ordinary English adjective for an undivided whole. The other named the numbers that have no fractional part. Both still mean, at bottom, something left untouched.