word forming element indicating "oneself," also "automatic," from Old English use of self (pron.) in compounds, such as selfbana "suicide," selflice "self-love, pride, vanity, egotism," selfwill "free will."
1856, "having or indicating reliance or confidence;" see rely (v.) + -ant. Perhaps based on reliance. Because its meaning shades into "dependent (on)," a sense attested by 1878, it would seem an odd name for an automobile, but Chrysler (Plymouth) nonetheless chose it as one in 1981.
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Definitions of self-reliant from WordNet
(of persons) free from external control and constraint in e.g. action and judgment;