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1706, with suffix -ous, from Modern Latin isochronus, from Greek isokhronos "equal in time," from iso- "equal" (see iso-) + khronos "time" (see chrono-). Earlier in same sense was isochronal (1670s).
isochronous i·soch·ro·nous (ī-sŏk'rə-nəs)adj. Occurring during the same time.