Etymology
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interval (n.)

early 14c., "time elapsed between two actions or events," from Old French intervalle "interval, interim" (14c.), earlier entreval (13c.) and directly from Late Latin intervallum "a space between, an interval of time, a distance," originally "space between palisades or ramparts" [OED], from inter "between" (see inter-) + vallum "rampart, palisade, wall," which is apparently a collective form of vallus "stake," from PIE *walso- "a post" (see wall (n.)).

Metaphoric sense of "gap in time" also was in Latin. From c. 1400 in English as "a pause, an interruption in a state or activity." Musical sense "difference in pitch between two tones" is from c. 1600. Related: Intervallic.

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intermissive (adj.)

"not continuous," 1580s, from Latin intermiss-, past-participle stem of intermittere "leave off, leave an interval" (see intermit).

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semitone (n.)

late 15c., semiton, "a musical interval approximating one-half of a whole tone," what we would call a minor second, the smallest interval in ordinary scales, from Old French semiton and directly from Medieval Latin semitonus; see semi- + tone (n.) in the musical sense. In art, in reference to tints, by 1782. Related: Semitonal (1863); semitonic (1728).

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in-between (n.)

1815, "an interval;" also "a person who intervenes," noun use of prepositional phrase, from in (adv.) + between. Related: In-betweener (1912); in-betweenity (1927).

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interstitial (adj.)

"pertaining to or situated in an interstice," 1640s, from Latin interstitium "interval" (see interstice) + -al (1). Related: Interstitially.

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augmented (adj.)

c. 1600, "increased," past-participle adjective from augment. The musical sense of "greater by a semitone than a perfect or major interval" (opposite of diminished) is attested by 1825.

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meantime (n.)

also mean time, mid-14c., mene-time, "interim, interval between one specified time and another" (now only in in the mean time), from mean (adj.2) "middle, intermediate" + time (n.). Late 14c. as an adverb, "during the interval (between one specified time and another)." As a noun, properly written as two words but commonly as one, after the adverb. In the mean space "meanwhile" was in use 16c.-18c.

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unison (n.)

1570s, "note having the same pitch as another; identity in pitch of two or more sounds; interval between tones of the same pitch," especially the interval of an octave, from French unisson "unison, accord of sound" (16c.) or directly from Medieval Latin unisonus "having one sound, sounding the same," from Late Latin unisonius "in immediate sequence in the scale, monotonous," from Latin uni- "one" (from PIE root *oi-no- "one, unique") + sonus "sound" (from PIE root *swen- "to sound"). Figurative sense of "harmonious agreement" is first attested 1640s.

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parsec (n.)

interstellar distance measure, 1913, from first elements of parallax second. It is the distance at which an object has parallax (viewed from Earth at an interval of six months and halved) of one second of arc, or about 3.26 light-years.

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interstice (n.)

early 15c., from Old French interstice (14c.) and directly from Latin interstitium "interval," literally "space between," from inter "between" (see inter-) + stem of stare "to stand" (from PIE root *sta- "to stand, make or be firm"). Related: Interstices.

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