The Collaborative International Dictionary of English v.0.48:

mendelevium \men*de*le"vi*um\ (m[e^]n*d[e^]*l[=e]"v[=e]*[u^]/m),
   a. [From Dmitri Mendeleyev, discoverer of the periodic law.]
   (Chem.)
   an unstable radioactive element discovered in 1955 and
   produced artificially only in very small quantities; symbol
   Md (also Mv). It is a transuranic element with atomic number
   101. Isotopes 255, 256, 257, and 258 have been prepared.
   Md258, the longest-lived, has a half-life of two months.
   --HCP61
   [PJC]

WordNet (r) 3.0 (2006):

mendelevium
    n 1: a radioactive transuranic element synthesized by bombarding
         einsteinium with alpha particles (Md is the current symbol
         for mendelevium but Mv was formerly the symbol) [syn:
         mendelevium, Md, Mv, atomic number 101]