the.com/girlfriend

means A woman in an ongoing romantic relationship with someone, often implying a degree of commitment short of marriage.

from A straightforward compound of 'girl' and 'friend,' first used in the 19th century simply to mean a female friend. It narrowed over the early 20th century into the romantic-partner sense we use today, as 'friend' itself had long carried a euphemistic whiff of courtship (compare the older use of 'friend' for a lover).