1630s, "part of a Middle Eastern house reserved for women," from Turkish harem, from Arabic haram "wives and concubines," originally "women's quarters," literally "something forbidden or kept safe," from root of harama "he guarded, forbade." From 1784 in English as "wives, female relatives and female slaves in a Middle Eastern household." The harem-skirt was introduced in fashion 1911. Harem pants attested from 1921; fashionable c. 1944. An earlier word for them (in a Middle Eastern/Balkan context) was bag-trousers (1849).
<a href="https://www.etymonline.com/word/haram">Etymology of haram by etymonline</a>
Harper, D. (n.d.). Etymology of haram. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/haram