Bachelorette

Bachelorette (pronounced bach-uh-luh-ret or bach-luh-ret)

(1) An unmarried young woman.

(2) In Canada, a term for a small apartment suitable for a single man.

1935: Some sources date the word from 1895 but it appears more likely bachelor-girl was first seen in 1888 and bachelorette is an American invention first noted in 1935.  Root is bachelor which came from the Middle English bachelor, derived from Anglo-Norman bacheler which exists in modern French as bachelier.  The Medieval Latin baccalārius was from Late Latin baccalāris and the Tuscan baccalare.  Ultimate source is a bit murky and strangely, although Old French had bachelette (young girl) in the 1400s, it's something English seems never to have borrowed.

Once were spinsters

Neither bachelor-girl (1888) nor bachelorette (1935) can really be considered proto-feminist because neither replaced spinster; merely re-defined as something applied to older un-married women; in the shifting hierarchy of misogyny, ageism prevailed.  It may thus be thought casual, female-specific ageism, especially because older, un-married men remain described as bachelors even if centenarians.  It’s not clear when spinster came to be thought of as disparaging and offensive but the usage certainly declined with rapidity after World War II and both it and bachelor have effectively been replaced with the gender-neutral single although in English common-law, the older forms lasted until 2005.

There's another quirk.  Middle French had the unrelated bachelette (young girl) which persists in the Modern French bachelière but that applies exclusively to students.  In the narrow technical sense, still sometimes insisted upon in British circles, a more proper neologism would be bacheloress, since -ess is the usual English suffix denoting a female subject, while -ette is a French-origin diminutive suffix, traditionally used to describe something smaller in size.  However, bachelorette was invented in the US where the -ette suffix can indicate a feminine version of a noun without implying a change in size.

In these gender-conscious times, the -ess suffix is anyway falling into disuse due to attempts to neutralize professional terms.  Except for historic references, it’s probably now obsolete.

Noted bachelorette Lindsay Lohan.