"purpose," O.E.
sacu "a cause at law, crime, dispute, guilt," from P.Gmc.
*sako "affair, thing, charge, accusation" (cf. O.N.
sök "charge, lawsuit, effect, cause," O.Fris.
seke "strife, dispute, matter, thing," Du.
zaak, Ger.
sache "thing, matter, affair, cause"), from PIE base
*sag- "to investigate" (cf. O.E.
secan, Goth.
sokjan "to seek;" see
seek). Much of the word's original meaning has been taken over by
case, cause, and it survives largely in phrases
for the sake of (c.1225) and
for _______'s sake (c.1300, originally
for God's sake), both probably are from O.N., as these forms have not been found in O.E.
[sak-ee, sah-kee] 
