Involuntary

wiktionary

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From in- +‎ voluntary, from Late Latin involontarius, from in + volontarius.

etymonline

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involuntary (adj.)

mid-15c., from Late Latin involuntarius "involuntary, unwilling," from in- "not, opposite of" (see in- (1)) + Latin voluntarius "willing, voluntarily" (see voluntary). Related: Involuntarily.