parterre (n.)

1620s, "equality in value or circumstances," also "value of one currency in terms of another," from Latin par "equal, equal-sized, well-matched," also as a noun, "that which is equal, equality," a word of unknown and disputed origin. De Vaan is noncommittal. Watkins suggests perhaps from PIE root *pere- (2) "to grant, allot," with suggestion of reciprocality. Another guess connects it with PIE root *per- (5) "to traffic in, sell" (on notion of "give equal value for"). Meaning "a standard fixed by consent or by natural conditions, average or usual amount" is first attested 1767. Golf sense is attested by 1898, which led to the figurative use of par for the course for "fairly normal, what can be expected" (by 1928).

1727, "ground for training horses," from French terrain "piece of earth, ground, land," from Old French (12c.), from Vulgar Latin *terranum, from Latin terrenum "land, ground," noun use of neuter of terrenus "of earth, earthly," from terra "earth, land," literally "dry land," as opposed to "sea" (from PIE root *ters- "to dry").

A dictionary word originally, little used in English except as a French word before it emerged from c. 1825 in the scientific meaning "part of the earth's surface," especially "tract of country considered with regard to its natural features or fitness for some use" (1766) via its use in translations from geologists writing in French.

We have no word in the English language that will accurately express terrain, as used in geology by the French : it here means a series of formations : but sometimes also terrain denotes a tract or district consisting of a particular class of rocks. [translator's note in English edition of Humboldt's " Essai Geognostique sur le Gisement des Roches dans les deux Hémisphères," London, 1823]

Middle English had terrage "land, ground" (c. 1400), from Old French or Medieval Latin, also terreoir "land, territory" (mid-15c.) from Old French terreior.

Proto-Indo-European root meaning "to dry."

It forms all or part of: inter; Mediterranean; metatarsal; parterre; subterranean; tarsal; tarsus; Tartuffe; terra; terrace; terra-cotta; terrain; terran; terraqueous; terrarium; terrene; terrestrial; terrier; territory; thirst; toast; torrent; torrid; turmeric; tureen.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit tarsayati "dries up;" Avestan tarshu- "dry, solid;" Greek teresesthai "to become or be dry," tersainein "to make dry;" Latin torrere "dry up, parch," terra "earth, land;" Gothic þaursus "dry, barren," Old High German thurri, German dürr, Old English þyrre "dry;" Old English þurstig "thirsty."