The problem with using the word gender to represent how one feels psychologically and sex for the biological differences is that historically, gender and sex are synonyms. It became popular in the Victorian era because that lot of prudes didn't want to say the word "sex," which could also mean reproductive and erotic behavior. People who throw "gender reveal" parties are using it according to its historical intent. Gender as psychological identity is still a niche definition.
Changing an existing word's meaning is often a fraught enterprise. Once it becomes a political football, it degenerates into a fight over who controls the language.
c. 1300, "kind, sort, class, a class or kind of persons or things sharing certain traits," from Old French gendre, genre "kind, species; character; gender" (12c., Modern French genre), from stem of Latin genus (genitive generis) "race, stock, family; kind, rank, order; species," also "(male or female) sex," from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.
The "male-or-female sex" sense of the word is attested in English from early 15c. As sex (n.) took on erotic qualities in 20c., gender came to be the usual English word for "sex of a human being," in which use it was at first regarded as colloquial or humorous. Later often in feminist writing with reference to social attributes as much as biological qualities; this sense first attested 1963. Gender-bender is from 1977, popularized from 1980, with reference to pop star David Bowie.
- https://www.etymonline.com/