The modern concept of "gender" was introduced to be distinct from that of "sex", but the word dates back to Latin at least and, until repurposed, it was synonym

The modern concept of "gender" was introduced to be distinct from that of "sex", but the word dates back to Latin at least and, until repurposed, it was synonymous despite the strong specialization towards use in grammar: the gender of nouns, pronouns, articles etc. is aligned with the sex of things. Of course, the aspect of cultural arbitrariness of grammatical gender (with different languages assigning a different gender to corresponding words) leads directly to the new psychological meaning of the word.