WordNet (r) 3.0 (2006):

atomic number 11
    n 1: a silvery soft waxy metallic element of the alkali metal
         group; occurs abundantly in natural compounds (especially
         in salt water); burns with a yellow flame and reacts
         violently in water; occurs in sea water and in the mineral
         halite (rock salt) [syn: sodium, Na, atomic number
         11]