The Collaborative International Dictionary of English v.0.48:

Libra \Li"bra\ (l[imac]"br[.a]), n.; pl. Libr[ae]
   (l[imac]"br[=e]). [L., a balance.] (Astron.)
   (a) The Balance; the seventh sign in the zodiac, which the
       sun enters at the autumnal equinox in September, marked
       thus [libra] in almanacs, etc.
   (b ) A southern constellation between Virgo and Scorpio.
        [1913 Webster]