The Collaborative International Dictionary of English v.0.48:

Hetaera \He*t[ae]"ra\, Hetaira \He*tai"ra\, n.; pl. -r[ae].
   [NL. See Hetairism.] (Gr. Antiq.)
   A female paramour; a mistress, concubine, or harlot. --
   He*t[ae]"ric, He*tai"ric, a.
   [Webster 1913 Suppl.] Hetairism