early 15c., "one and indivisible, inseparable" (with reference to the Trinity), from Medieval Latin individualis, from Latin individuus "indivisible," from in- "not, opposite of" (see in- (1)) + dividuus "divisible," from dividere "divide" (see divide (v.)). Original sense now obsolete; the word was not common before c. 1600 and the 15c. example might be an outlier. Sense of "single, separate, of but one person or thing" is from 1610s; meaning "intended for one person" is from 1889.
Individual views a person as standing alone, or persons as standing separately before the mind: as, the rights of the individual; the rights of individuals: it is incorrect to use individual for person unemphatically ; as, there were several individuals in the room. [Century Dictionary]
"quality of being distinct or individual, individuality," 1815, from individual + -ism. As the name of a social philosophy favoring non-interference of government in lives of individuals (opposed to communism and socialism) first attested 1851 in writings of J.S. Mill.
Is it not the chief disgrace in the world, not to be an unit; not to be reckoned one character; not to yield that peculiar fruit which each man was created to bear, but to be reckoned in the gross, in the hundred, or the thousand, of the party, the section, to which we belong; and our opinion predicted geographically, as the north or the south? [Emerson, "The American Scholar," 1837]