William Leap, a professor of anthropology at American University who studies the field of “lavender linguistics,” which examines how gay people use certain words and phrases, said the offensiveness of the word stems from its medical history. “It already has all that clinical baggage heaped on it: that’s the legacy of the term now,” he said, adding that because of its use in a scientific way, many people do not realize how it can fall on gay and lesbian ears.

“It’s not like ‘faggot,’ which is a negative term that could get somebody’s mother to slap their hand,” he said. “Homosexual is a term that everybody knows.”

Yet it endures.

“Now they’re encouraging this young man who’s announced he’s homosexual to go play, when Obama said he wouldn’t even let his own son play,” Rush Limbaugh said recently as he talked about Michael Sam, the college football player who recently came out. When Gov. Jan Brewer of Arizona faced pressure to veto a bill that would have allowed businesses to refuse service to gay and lesbian customers, Mr. Limbaugh cited the work of the “homosexual lobby.”

And last year, when Jason Collins became one of the first professional male athletes to reveal he was gay, Chris Broussard, an ESPN commentator who has called homosexuality “that lifestyle” and condemned it as a sin, announced that he had “no problem with homosexuals.” Later, an article in The Christian Post described his comments, noting that Mr. Broussard went on to discuss his conversations on the subject with a gay colleague, LZ Granderson, whom the writer noted is “a homosexual ESPN commentator.”

During oral arguments last year in the Supreme Court case Hollingsworth v. Perry, when Justice Antonin Scalia asked the lawyer Ted Olson, “When did it become unconstitutional to prohibit homosexuals from marrying?” it seemed to some that he was unable (or unwilling) to use the word gay.

The word’s power depends, of course, on who is using it. In the late 1970s, Anita Bryant’s “Save Our Children” campaign was centered on the notion of “homosexual recruitment,” the belief that gays and lesbians tried to woo unsuspecting children into their ranks. Gerry E. Studds, the first openly gay member of Congress, once recalled how someone confronted him about whether he was still a “practicing homosexual.” He shot back: “No. As a matter of fact, I think I’m very good at it.”