The Collaborative International Dictionary of English v.0.48:

Aquamarine \A`qua*ma*rine"\, n. (Min.)
   A transparent, pale green variety of beryl, used as a gem.
   See Beryl.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Beryl \Ber"yl\ (b[e^]r"[i^]l), n. [F. b['e]ryl, OF. beril, L.
   beryllus, Gr. bh`ryllos, prob. fr. Skr. vai[dsdot][=u]rya.
   Cf. Brilliant.] (Min.)
   A mineral of great hardness, and, when transparent, of much
   beauty. It occurs in hexagonal prisms, commonly of a green or
   bluish green color, but also yellow, pink, and white. It is a
   silicate of aluminum and beryllium. The aquamarine is a
   transparent, sea-green variety used as a gem. The emerald
   is another variety highly prized in jewelry, and
   distinguished by its deep color, which is probably due to the
   presence of a little oxide of chromium.
   [1913 Webster]

WordNet (r) 3.0 (2006):

aquamarine
    n 1: a transparent variety of beryl that is blue green in color
    2: a shade of blue tinged with green [syn: greenish blue,
       aqua, aquamarine, turquoise, cobalt blue, peacock
       blue]