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.