The Collaborative International Dictionary of English v.0.48:

Hetairism \He*tair"ism\, Hetarism \Het"a*rism\, n. [Gr. ? a
   companion, a concubine, fem. of ? a comrade.]
   A supposed primitive state of society, in which all the women
   of a tribe were held in common. --H. Spencer. --
   Het`a*ris"tic, a.
   [1913 Webster]