Neo- \Ne"o-\ [Gr. ? youthful, new. See New.]

A prefix meaning new, recent, late; and in chemistry designating specifically that variety of metameric hydrocarbons which, when the name was applied, had been recently classified, and in which at least one carbon atom in connected directly with four other carbon atoms; -- contrasted with normal and iso-; as, neopentane; the neoparaffins. Also used adjectively.

Source: Webster's Revised Unabridged Dictionary (1913)