Etymology
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medial (adj.)

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.

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medial (n.)
"a medial letter," 1776, from medial (adj.).
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medially (adv.)

"in a medial or central position," 1804, from medial (adj.) + -ly (2).

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Midi 

"southern France," 1883, from French midi "south," literally "midday" (12c.), from mi "middle" (from Latin medius "middle;" see medial (adj.)) + di "day" (from Latin dies, from PIE root *dyeu- "to shine"). At midday in the northern hemisphere the sun is in the south of the sky. Compare Latin meridianus "of midday, of noon;" also "southerly, to the south" (see meridian), and Middle English mid-dai in its secondary sense "south, to the south" (late 14c.).

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mitten (n.)

late 14c., mitain (from mid-13c. in surnames) "a glove, a covering for the hand," especially "a covering for the hand, differing from a glove in not having a separate covering for each finger, the thumb only being separated," from Old French mitaine "mitten, half-glove" (12c.) and from Medieval Latin mitta, both of uncertain origin; both perhaps from Middle High German mittemo, Old High German mittamo "middle, midmost" (reflecting the notion of "half-glove"), or from Vulgar Latin *medietana "divided in the middle," from Latin medius (see medial (adj.)).

From 1755 as "lace or knitted silk glove for women covering the forearm, the wrist, and part of the hand," worn fashionably by women in the early 19c. and revived towards the end of it. Hence get the mitten (1825), of men, "be refused or dismissed as a lover" (colloquial), from the notion of receiving the mitten instead of the "hand."

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stave (n.)
"piece of a barrel," 1750, back-formation from staves (late 14c.), plural of staff, with the usual change of medial -f- to -v- (compare leaves/leaf). The plural form possibly was in Old English but not recorded there.
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meson (n.)

subatomic particle, 1939, from Greek mesos "middle" (from PIE root *medhyo- "middle") + subatomic particle suffix -on. Earlier mesotron (1938). So called for being intermediate in mass between protons and electrons. An earlier use of the word, from the Greek noun meson "center," meant "the medial plane which divides the body into two equal and symmetrical parts" (by 1883).

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thither (adv.)
Old English þider "to or toward that place," altered (by influence of its opposite hider) from earlier þæder "to that place," from Proto-Germanic *thadra- (source also of Old Norse þaðra "there," Gothic þaþro "thence"), from PIE pronominal root *to- (see that) + PIE suffix denoting motion toward (compare Gothic -dre, Sanskrit -tra). The medial -th- developed early 14c. but was rare before early 16c. (compare gather, murder, burden).
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grave (v.)
"to engrave," Old English grafan "to dig, dig up; engrave, carve, chisel" (medial -f- pronounced as "v" in Old English; past tense grof, past participle grafen), from Proto-Germanic *grabanan (source also of Old Norse grafa "to dig; engrave; inquire into," Old Frisian greva, Dutch graven "to dig, delve," Old High German graban, German graben, Gothic graban "to dig, carve"), from the same source as grave (n.). Its Middle English strong past participle, graven, is the only part still active, the rest of the word supplanted by its derivative, engrave.
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fortress (n.)

early 14c., from Old French forteresse, forterece "strong place, fortification" (12c.), variant of fortelesse, from Medieval Latin fortalitia, from Latin fortis "strong" (see fort) + -itia, added to adjectives to form nouns of quality or condition. French -ess from Latin -itia also is in duress, largesse, riches, also obsolete rudesse, "lack of cultivation" (early 15c.).

For change of medial -l- to -r- in Old French, compare orme "elm" from Latin ulmus; chartre from cartula; chapitre from capitulum.

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