Meta- \Met"a-\, Met- \Met-\ [Gr. ? between, with, after; akin to AS. mid with, G. mit, Goth. mi[thorn], E. mid, in midwife.]

1. A prefix meaning between, with, after, behind, over, about, reversely; as, metachronism, the error of placing after the correct time; metaphor, lit., a carrying over; metathesis, a placing reversely.

2. (Chem.) A prefix denoting:
   (a) Other; duplicate, corresponding to; resembling; hence, metameric; as, meta-arabinic, metaldehyde.
   (b) (Organic Chem.) That two replacing radicals, in the benzene nucleus, occupy the relative positions of 1 and 3, 2 and 4, 3 and 5, 4 and 6, 5 and 1, or 6 and 2; as, metacresol, etc. See Ortho-, and Para-.
   (c) (Inorganic Chem.) Having less than the highest number of hydroxyl groups; -- said of acids; as, metaphosphoric acid. Also used adjectively.

Source: Webster's Revised Unabridged Dictionary (1913)