Old English forsacan "object to, oppose, refuse, deny; give up, renounce" (past tense forsoc, past participle forsacen), from for- "completely" + sacan "to struggle, dispute, wrangle; accuse, blame" (see sake (n.1)). Related: Forsaking. Similar formation in Old Saxon farsakan, Dutch verzaken, Old High German farsahhan "deny, repudiate," Danish forsage "give up, refuse."
Forsake is chiefly applied to leaving that by which natural affection or a sense of duty should or might have led us to remain: as, to forsake one's home, friends, country, or cause; a bird forsakes its nest. In the passive it often means left desolate, forlorn. [Century Dictionary]