This word with its grammatical variants is at the root of our hermeneutical difficulties, in my opinion. It was first coined in 1869 “in two anonymous German pamphlets published by Karoly Maria Kertbeny” (Enc. Hom. I:555), and popularized in 1880 by Stuttgart professor Gustav Jaeger. John Boswell discovered an English usage from 1891 in John Addington Symonds, A Problem in Modern Ethics (see CSTH 42 n.4), although the first incidence cited by the Oxford English Dictionary at the time had been from 1899. It gained currency in most European languages by 1907, in connection with reportage of the Eulenburg Affair, and eclipsed the host of competing coinages that had arisen in the last half of the 19th century: sexual inversion, uranism, contrary sexual feelings, and others.
Semantic problems: it is, as has often been noted, a hybrid of “Greek prefix and Latin root” (CSTH 41). The fact that the Greek combining form of ‘homos’ = “same” is identical to the Latin word ‘homo’ = “man” has led to distortions in the popular mind: that it always refers to male-to-male sexual contact – so that some lesbians have rejected its application to them for obvious, if mistaken, reasons. (A recent MennoLink exchange I had confirms my belief that this very misunderstanding is at the root of much popular discomfort with “homosexuality” – my interlocutor complained that his dictionary quite clearly defined “homo” as Latin for “man,” and therefore I must be mistaken about its Greek origin and the meaning “same.”)
What part of speech is ‘homosexual’? Kertbeny coined it as an adjective (he used Homosexualitaet and Homosexualismus as nouns for the characteristic, but did not speak of individual persons as homosexuals). Over the years into the 20th century the formation “homosexual person” became elided into “homosexual” as a noun, creating by means of language a class of human being that had never existed before: anyone of whatever biological gender who engaged in sexual activity with someone of the same gender.
Hermeneutical problem: so many disparate kinds of behavior and ways of life have been lumped together under this one term that it is easy for people to overlook the many gradations of social and moral acceptability that can be found within its tent. The problem would not be quite so bad if “heterosexual” were applied with equal abandon to all kinds of opposite-sex genital behavior, from child molestation to prostitution to rape, but those kinds of behavior, when engaged in heterosexually, are usually denominated by those specific names rather than as forms of heterosexuality. What becomes even worse is that heterosexual child molestation, e.g., is often itself called “homosexuality” by the uninformed and misled. It has become a blanket term for anything thought disgusting; for all kinds of “immorality.”
Recommended practice: avoid the use of these forms whenever a more specific and accurate alternative exists. Resist the impulse to collectivize unrelated phenomena into an artificial class. Possible alternatives if a collective term is absolutely required are GLBT (gay/lesbian/bisexual/transgender), SEXUAL MINORITIES (see Glossary), SAME-SEX.