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