in music, "third note of the diatonic scale" (the one which determines whether the scale is major or minor), 1753, from Italian mediante, from Late Latin mediantem (nominative medians) "dividing in the middle," present participle of mediare "to be in the middle," from Latin medius "middle" (from PIE root *medhyo- "middle"). So called from being midway between the tonic and the dominant.
mid-14c., mediatour, "one who intervenes between two parties (especially to seek to effect a reconciliation)," from Late Latin mediator "one who mediates," agent noun from stem of mediare "to intervene, mediate," also "to be or divide in the middle," from Latin medius "middle" (from PIE root *medhyo- "middle"). Originally applied to Christ, who in Christian theology mediates between God and man. Meaning "one who intervenes between two disputing parties for the purpose of effecting reconciliation" is first attested late 14c. Feminine form mediatrix (originally of the Virgin Mary) from c. 1400. Related: Mediatorial; mediatory.
1560s, "pertaining to a mathematical mean," from Late Latin medialis "of the middle," from Latin medius "in the middle, between; from the middle," as a noun (medium) "the middle;" from PIE root *medhyo- "middle." Meaning "occupying a middle position, existing between two extremities or extremes" is attested from 1721.
"pertaining to or situated in the middle, occupying a middle or intermediate position," 1590s, from French médian (15c.) and directly from Latin medianus "of the middle," from medius "in the middle" (from PIE root *medhyo- "middle"). Originally anatomical, of veins, arteries, nerves; general use is by 1640s. Median strip "narrow strip (paved or not) between lanes of a divided road" is by 1939, American English.
1540s, "divide in two equal parts" (a sense now obsolete), from Latin mediatus, past participle of mediare "to halve," later, "be in the middle," from Latin medius "middle" (from PIE root *medhyo- "middle"); from 1640s as "occupy a middle place or position." Meaning "act as a mediator, intervene for the purpose of reconciliation" is from 1610s; that of "settle by mediation, harmonize, reconcile" is from 1560s, perhaps back-formations from mediation or mediator. Related: Mediated; mediates; mediating.
early 15c., "intermediate," from Medieval Latin mediatus, past-participle adjective from Latin mediare "to be in the middle," from medius "middle" (from PIE root *medhyo- "middle"). Related: Mediately.
early 15c., trophe, "an overwhelming victory;" 1510s, "a spoil or prize of war," from Old French trophée (15c.) from Latin trophaeum "a sign of victory, monument," originally tropaeum, from Greek tropaion "monument of an enemy's defeat," noun use of neuter of adjective tropaios "of defeat, causing a rout," from trope "a rout," originally "a turning" (of the enemy); from PIE root *trep- "to turn."
In ancient Greece, spoils or arms taken in battle and set up on the field and dedicated to a god. Figurative extension to any token or memorial of victory is first recorded 1560s. As "a symbolic representation of a classical trophy" from 1630s.
Trophy wife "a second, attractive and generally younger, wife of a successful man who acquires her as a status symbol" was a trending phrase in media from 1988 ("Fortune" magazine did a cover story on it in 1989), but is older in isolated instances.
Variations on this theme ['convenience-wife'] include the HOSTESS-WIFE of a businessman who entertains extensively and seeks a higher-level, home-branch version of his secretary; the TROPHY-WIFE — the woman who was hard to get because of birth or wealth or beauty — to be kept on exhibition like a mammoth tusk or prime Picasso ... [Phyllis I. Rosenteur, excerpt from "The Single Women," published in Philadelphia Daily News, Dec. 12, 1961]
The excerpt distinguishes the trophy wife from the "showcase wife," "chosen for her pulchritude and constantly displayed in public places, dripping mink and dangling diamonds," which seems more to suit the later use of trophy wife.