What English speakers do with it now
In ordinary English, to finish something is to bring it to its last point: a meal, a sentence, a job, a race. The intransitive use is just as common. A concert finishes; a meeting finishes late. As a noun, finish can mean that last point itself, the protective coating on wood or metal, the last taste a wine leaves in the mouth, or the shot that puts a ball in the net. The shared idea is an edge. The word names the place where a process stops being unfinished.
English already had older ways to say that something came to an end. What it borrowed in the later Middle Ages was a Romance verb whose older Latin sense was a boundary on the ground.
A French stem, not an English suffix
The origin of the word finish is a borrowing from French. It is not inherited from Old English. Speakers of Old English used native verbs such as endian for reaching an end. The new form arrived as Middle English finishen, finisshen, and finischen, taken from the lengthened stem of Old French fenir, later spelled finir.
That stem is the key to the English shape. French second-conjugation verbs in -ir insert -iss- in many forms: finissant, nous finissons, ils finissent. English copied the stem finiss- (older sources also give feniss-), not the bare infinitive. The result looks as if it contained the familiar English adjective ending of childish or greenish. It does not. The same French pattern gave nourish from nourrir and punish from punir. If English had taken only the infinitive, the verb would more likely have resembled fine.
The Oxford English Dictionary treats the verb as a French loan and dates its earliest evidence before 1375, in the Middle English romance William of Palerne. Independent etymological summaries put the transitive sense, to bring to an end, in the late fourteenth century, and the intransitive sense, to come to an end, in the mid-fifteenth. Old French fenir already covered stopping, coming to an end, and dying. English inherited that range and then stretched it.
From a Roman boundary to a Latin verb
Behind the French verb stands Latin finire: to set a limit, to put an end to something, or to come to an end oneself. The verb is built on the noun finis, which first named a dividing line. In Classical Latin the word could mean a border, a frontier, or the edge of a plot of land. In the plural, fines often meant the territory inside those borders. From the physical line the noun moved, still in Latin, to a limit in time, to death as the close of a life, and to purpose or aim: the point toward which an action is directed.
That last sense is easy to miss in modern English finish, which is about stopping rather than intending. It survives more clearly in related words. Final and finite keep the idea of a bound. Define and confine keep the idea of drawing a line around something. Fine as an adjective of quality comes from the same noun by way of Old French, through the notion of a highest point or perfected state. Fine as a penalty comes from the idea of settling a matter, bringing a legal debt to its close. Finance belongs to that family as well. These are siblings of finish, not later offshoots of the English verb.
Romance languages keep the noun close to Latin: French fin, Italian fine, Spanish fin, Portuguese fim, Catalan fi. The verbs travel with them: French finir, Italian finire. English later sent the sports noun the other way. Dutch finish, Polish finisz, and Russian финиш are loans from English, used especially of a race, not independent inheritances of Latin finis.
An unknown deeper root
Whether Latin finis has a secure Indo-European ancestor is an open question. Standard references mark the ultimate origin as unknown. One proposal links the noun to Latin figere, to fasten or drive in, as if a boundary were first a stake fixed in the ground, going back to a root meaning to stick or set up. Another reconstructs an older *fidnis and connects it with findere, to split, as if a limit were a cut. None of these accounts is agreed. The picture of a boundary marker is attractive, but it is a hypothesis, not the documented history of the English word.
How the senses widened
Once the verb was at home, English used it along a line from stopping to completing. Speakers could finish a task in the sense of going through its last stage, or finish food and drink in the sense of using up what remained. They could also finish an object by putting the last detailed work on it. A rare and short-lived sense, closer to the Latin verb, was to assign a boundary to something. That use did not last.
A harsher extension is recorded from the mid-eighteenth century: to kill, or to terminate someone’s existence. The same logic later appears in combat sports, where a finish is a knockout or submission that ends a bout before the clock does. In weaker colloquial use, a rumour can finish a career without anyone dying.
The noun is late compared with the verb. It is recorded from 1779 as that which gives completion, and from 1790 as the end itself. Finish line is attested from 1873. The surface sense, the last treatment on wood, metal, or paint, is completion made visible: the process that determines how an object looks when nothing more is to be done to it. Builders used the same idea for the finer interior work that completes a house. Finishing school, recorded in the early nineteenth century, treats social polish as the last coat of an education.
The edge the spelling still shows
The useful fact to keep is the extra syllable. English finish looks native and adjectival, but the -ish is a fossil of French verb class, and the root behind it is a Latin word for a border. Every ordinary use still sits on that older line: the point at which a thing is no longer in progress, whether the thing is a sentence, a race, a coat of varnish, or a life.