The Collaborative International Dictionary of English v.0.48:

Neo- \Ne"o-\ [Gr. ne`os 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 is
   connected directly with four other carbon atoms; --
   contrasted with normal and iso-; as, neopentane; the
   neoparaffins. Also used adjectively.
   [1913 Webster]