Residual

wiktionary

ref

Recorded since 1570. From residue, itself from Old French residu (Modern résidu), from Latin residuum(“a remainder”), the neuter inflection of residuus(“remaining, left over”), perfect participle of resideō(“I remain behind”) (from re-(“back, again”) + sedeō(“I sit, I reside”).

etymonline

ref

residual (adj.)

"formed by subtraction of one quantity from another, of or like a residuum," 1560s, from residue + -al (1), or from French résiduel, from Latin residuum "that which is left behind." By c. 1600 as "remaining, left over."

residual (n.)

1550s, in mathematics, "a residual quantity," from residual (adj.) or from residue + -al (2). Residuals "royalties for repeated performance or broadcast" is attested by 1960.