What English does with it now
In current English, salient names what stands out. The salient points of a brief are the ones a reader is meant to keep. A salient trait is conspicuous rather than background. Used as a noun, the same spelling still has a more physical job: a bulge in a battle line, a trench that pushes into enemy ground, a national border that pokes into a neighbor. Both jobs share an image of something leaping forward. That image is not a late stylistic flourish. It is the older meaning of the adjective, and it is why a military salient looks the way it does on a map.
Onto English through a coat of arms
The origin of the word salient is easiest to see in heraldry. In the 1560s English armorists needed a term for a beast shown in mid-leap, hind feet on the ground and forepaws raised together. The posture is close to rampant, but not the same: a salient animal is caught springing, not standing in a climb. The earliest dated English use is 1562, in Gerard Legh’s handbook Accedens of Armory. Historical dictionaries treat that as the first record, in the mid-sixteenth century. Some desk dictionaries start the adjective at 1646 instead. They are not so much contradicting the heraldic date as indexing a later, more general sense: animals that actually move by leaping, rather than animals painted as if they did.
The source is Latin saliens, accusative salientem, the present participle of salire, to leap or spring. English kept the participial ending as -ent, the regular outcome of Latin -ens, -entem in learned loans. The spelling, and some of the later geometry, were also pulled toward French saillant, from the same Latin verb through saillir. This is not a native Germanic inheritance. It is a sixteenth-century borrowing into a specialist vocabulary, one of the Latin technical words English absorbed in that century, and only afterwards a word of ordinary prose.
A family of leaps
The morphology is transparent once the Latin participle is in view. The stem is the leap; the ending is the ending English uses for many present-participial adjectives borrowed from Latin, the same piece that appears in adjacent or fluent. No hidden prefix is doing the work, and no folk analysis is required.
Salire left a large English family besides this one adjective. Sally, a rush out from a fortress, comes through French saillie. Assault and assail are leaps upon an opponent. Insult once meant to jump at someone; exult is to leap up in joy; result and resile are leaps back. Desultory remembers the rider who jumped from horse to horse. Somersault and sauté keep the leap more literally. Salacious goes back to Latin salax, used of animals fond of leaping and, by extension, of lust. Those are genuine relatives. Romance still shows the same participle close to the surface: French saillant, Italian and Spanish saliente. Salmon is sometimes explained as the leaping fish from the same verb. That story is old and neat, and specialists often set it aside as folk etymology, with Latin salmo more likely a Celtic loan.
Behind Latin, handbooks reconstruct a Proto-Indo-European root meaning to jump or spring, often written sel-. The shape of that root is not settled. Comparative dictionaries call the form uncertain, and the Latin etymologist Michiel de Vaan treats the vowel grade as unclear; a reconstructed pre-form with a syllabic l would not, on the usual rules, yield Latin sal-. What is firmer is a cluster of related verbs: Greek hallesthai and hallomai, to leap; Sanskrit forms for flowing, running, or hurrying; Middle Irish saltraim, I trample; Middle Welsh sathar, trampling. Those comparisons support a jumping root without forcing a single reconstructed spelling.
How the meaning moved
Once the participle was in English, writers stretched it from painted beasts to anything that sprang. In the mid-seventeenth century Thomas Browne used it of animals whose motion is a leap. Robert Boyle, in 1669, applied it to water jetting upward. Geometry and fortification took a different step. By the 1680s a salient angle was one that pointed outward, the opposite of a re-entrant angle; a 1686 siege narrative already has an outward salliant angle in the works around Buda. From the outward angle it was a short walk to any projecting part of a wall or earthwork. The noun in that military sense is recorded from 1828. By the 1860s it could name a bulge in a line of attack or defence — the usage that later made the Ypres and Spotsylvania salients famous.
The sense that now dominates ordinary prose, prominent or noteworthy, is younger than the leap and younger than the fortress. Some etymological dictionaries place it around 1840, citing Thomas Carlyle; the Oxford tradition puts the figurative use in the eighteenth century. The path most accounts give is not a vague drift from jumping to important. It runs through a set phrase, salient point, recorded from the 1670s. That phrase translates New Latin punctum saliens, a rendering of a remark in Aristotle’s work on animals about the first moving speck in an embryo, the heart that seemed already to leap. From the living point that starts an organism, the phrase came to mean the starting point of an argument or an enterprise. German made the same calque on its own as der springende Punkt, the springing point. Once a point could leap out as the thing that mattered, the adjective could do that work without the noun.
Heraldry still uses the old leap. Military English still uses the outward bulge. Everyday English kept the leap only as a figure: what is salient is what springs at the attention. Four and a half centuries after Legh’s leaping beast, that is the surviving motion.