The Collaborative International Dictionary of English v.0.48:

Sachem \Sa"chem\ (s[a^]"chem), n.
   A chief of a tribe of the American Indians; a sagamore. See
   Sagamore.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sachem
    n 1: a political leader (especially of Tammany Hall)
    2: a chief of a North American tribe or confederation
       (especially an Algonquian chief) [syn: sachem, sagamore]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "sachem":
   Dalai Lama, Establishment, Holy Roman Emperor, Inca, Kaiser, VIP,
   ardri, baron, bey, big gun, big man, big name, bigwig, boss, brass,
   brass hat, cacique, caesar, celebrity, cham, czar, dignitary,
   dignity, elder, father, figure, great man, important person,
   interests, kaid, keynoter, khan, lion, lords of creation, magnate,
   man higher up, man of mark, mikado, mogul, nabob, name, negus,
   notability, notable, padishah, panjandrum, pendragon,
   person of renown, personage, personality, pharaoh,
   pillar of society, policy maker, power, power elite, rig,
   ringleader, ruling circle, sagamore, shah, sheikh, shogun,
   somebody, something, standard-bearer, tenno, the great, the top,
   top brass, top people, tycoon, very important person, worthy