The Collaborative International Dictionary of English v.0.48:
Forgo \For*go"\, v. t. [imp. Forwent; p. p. Forgone; p. pr.
& vb. n. Forgoing.] [OE. forgan, forgon, forgoon, AS.
forg[=a]n, prop., to go past, hence, to abstain from; pref.
for- + g[=a]n to go; akin to G. vergehen to pass away, to
transgress. See Go, v. i.]
1. To pass by; to leave. See 1st Forego.
For sith [since] I shall forgoon my liberty
At your request. --Chaucer.
And four [days] since Florimell the court forwent.
2. to abstain from; to do without; to refrain from; to
renounce; -- said of a thing already enjoyed, or of one
within reach, or anticipated. See 1st forego, 2.
Note: This word in spelling has been confused with, and
almost superseded by, forego to go before.
Etymologically the form forgo is correct.
Moby Thesaurus II by Grady Ward, 1.0:
21 Moby Thesaurus words for "forgone":
abandoned, abjured, ceded, dispensed with, disposed of,
foreordained, forsworn, predecided, predestinate, predestined,
predetermined, preordained, recanted, released, relinquished,
renounced, retracted, sacrificed, surrendered, waived, yielded