A two-axis name
In present-day English, altazimuth names an instrument or a mounting that turns on two perpendicular axes. One axis is vertical, so the device can sweep around the horizon. The other is horizontal, so it can nod up and down. Those two motions match two older sky coordinates: altitude, the angular height of an object above the horizon, and azimuth, its bearing around the compass. Astronomers put telescopes on such mounts. Surveyors use larger versions to measure vertical and horizontal angles. The same geometry turns up on radio dishes, cameras, heliostats, and even camera tripods.
The word itself is not a medieval import. It is a 19th-century scientific coinage built from two English terms that had already been in the language for centuries. Dictionaries write it as altitude plus azimuth, with the first half clipped so the pair fits in one stem. Some handbooks call that a blend; others print alt(itude) plus azimuth. The morphology is the same either way. The alt- here is not a Latin prefix meaning high. It is simply English altitude cut short so it can sit against azimuth.
A Victorian clip
Merriam-Webster dates the English noun to 1851. American Heritage and several dictionaries in the same tradition give a slightly later window, 1855–60. The gap is small and typical of first-attestation work: the clipped form was in print by the 1850s. Collins and Oxford-style notes simply place it in the 19th century.
The instrument is a little older than the short name. At the Royal Observatory, Greenwich, George Biddell Airy had an altitude-and-azimuth telescope designed in the 1840s and brought into regular use in 1847. Contemporary accounts still used the full phrase. Within a few years English scientific vocabulary compressed that phrase into a single word. Merriam-Webster classifies the formation as international scientific vocabulary: a learned label coined in English (and parallel technical registers) rather than borrowed ready-made from French, Latin, or Arabic.
From the first print uses the noun could name the measuring instrument, a telescope sitting on such a mount, or the mounting type itself. It also appears attributively, as in altazimuth mount. Workshop spellings followed: hyphenated alt-azimuth, then the still shorter altaz and alt-az.
Two older English words
Both halves had been English since the late 14th century, long before anyone glued them together.
Altitude arrived through Middle English from Latin altitudo, height, built on altus, high. The Latin adjective is often explained as grown tall, from a verb family that includes alere, to nourish. Etymologists reconstruct a Proto-Indo-European root written *al- or *h₂el-, to grow or nourish, the same stock that feeds words for age and fostering in several branches. In English the earliest uses of altitude were astronomical: the elevation of a star or planet above the horizon. The everyday sense of vertical extent is recorded from the early 15th century. Learned cousins include French altitude and Italian altitudine, both taken from the Latin noun, and the simpler adjective behind Italian alto.
Azimuth took another road. Late Middle English borrowed it from Old French azimut, itself from Arabic as-sumūt, the ways or the directions, the plural of as-samt, way or direction. The same Arabic noun, in the phrase samt ar-ra’s, the way over the head, is the source of English zenith, after medieval-Latin scribes misread an m as the letters ni. Azimuth kept a cleaner path. It stayed a technical term for an arc along the horizon between the meridian and a vertical circle through a celestial object. Parallel loans are easy to spot: French azimut, Spanish azimut or acimut, German Azimut, Russian азимут, Polish azymut, Portuguese azimute. Arabic samt remains the ordinary word for that coordinate.
One uncertainty belongs to azimuth, not to the later compound. Some etymologists have wondered whether Medieval Latin scribes also heard Latin semita, a side path, in the Arabic word, because the sounds are close. That is a possible overlay, not a proven parent. The Arabic source of azimuth is not in serious dispute.
What the compound did next
Unlike many long-lived English words, altazimuth never wandered into figurative use. It did not come to mean a high point, a bearing in life, or anything of that sort. What changed is the object it could name.
Mid-Victorian usage centers on a measuring instrument: a telescope, or a theodolite-like device, that records both coordinates at once. Later astronomical writing uses the word for a mounting style, set against the equatorial mount, which tilts one axis toward the celestial pole so a single motor can track the sky. An altazimuth mount is mechanically simpler, but it must drive both axes at changing speeds, the field of view rotates as it tracks, and pointing straight at the zenith can jam the geometry. Large professional telescopes adopted computer-controlled altazimuth mounts anyway, because the steelwork is cheaper and the dome can be smaller. Amateur builders, especially of Dobsonian Newtonians, favored the same two-axis layout for the opposite reason: plywood, Formica, and Teflon bearings are enough.
Surveying kept a second, more specialized sense: a large, precise instrument for vertical and horizontal angles, akin to a theodolite but heavier. The clipped compound also traveled as a technical loan. French formed the adjective altazimutal. Polish has altazymut and Portuguese altazimute.
A date worth keeping
Altitude and azimuth are medieval scholarly words, one Latin and one Arabic by way of Old French, both in English by about 1400. The origin of the word altazimuth is much later: a Victorian clip of those two, first recorded around 1851, a few years after Airy’s Greenwich instrument had made the unclipped phrase routine. It is not a fossil from Arabic astronomy. It is a 19th-century workshop label for a two-axis mount, built from two much older sky terms.