Immediate is Latin in- , "not," plus mediatus, "in the middle" — literally "with nothing in between." The double m is the seam where the prefix assimilated: in- became im- before the m of the root, and English kept both letters. It belongs with accept, appear, collect and suffer in the class of words whose doubled consonant near the front marks a swallowed Latin prefix.
The original English sense, from the late 1300s, was strictly spatial: intervening or, in the negative, with nothing interposed, direct. The temporal sense — without delay — is barely later, from the early 1400s, and has almost entirely taken over. The spatial meaning survives in phrases like the immediate vicinity and in immediate family, where what is meant is that no other relatives stand in between.
immediate (adj.) late 14c., "intervening, interposed;" early 15c., "with nothing interposed; direct," also with reference to time, "without delay, instant," from Old French immediat (14c.), from Late Latin immediatus "without anything between," from assimilated form of in- "not, opposite of" (see in- (1)) + mediatus "in the middle" (see mediate ). Related: Immediateness . also from late 14c.
immediate came in through Latin, and its spelling follows that family's conventions.
How that family writes these sounds
| a consonant that sounds doubled just after a prefix | double it. The prefix assimilated to the root: ad+cept, ad+prove, in+mediate, com+lectaccept, approve, immediate, collect, suffer |
What gives it away on the page
| a doubled consonant after a short prefix | The prefix assimilated to the root: ad+cept, ad+prove, in+mediate, com+lect.accept, approve, immediate, collect, suffer |
Placing it without the spelling
| three or more syllables, stress in the middle, audibly assembled from parts | Latinimmediate, obstruct, various |