plain-Jane
adjective phrase

- not fancy or glamorous; ordinary

Merriam-Webster's Online Dictionary

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WORD ORIGIN

Plain-Jane originated in the U.S. in the 1930s. Jane has long been used as a synonym for any woman. Adding plain, which means ordinary and simple, paints the picture of a woman with average or unexceptional looks, usually without makeup or stylish clothing.

You may consider this a bit unfair to women, given that there is no male equivalent like plain Peter or plain Blaine.

Much has been written about society placing too much emphasis on outer beauty. According to the famous saying "beauty is only skin deep" meaning that real beauty lies in our soul, to which the American playwright Jean Kerr remarked:

"I'm tired of all this nonsense about beauty being only skin-deep. That's deep enough. What do you want, an adorable pancreas?"

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The adjective phrase plain-Jane (with a hyphen) describes any object that has no flair, colour, style, or special features. While this sometimes has a negative connotation, it is not always the case. A plain-Jane device can lack additional functions or a modern design, but still do the job it is intended for. 

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SYNONYMS

average, common, conventional, dull, garden variety, generic, habitual, mediocre, modest, normal, pedestrian, routine, run-of-the-mill, simple, so-so, undistinguished, uneventful, unexceptional, uninspired, unmemorable, unpretentious, unremarkable, usual, vanilla, workaday

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ANTONYMS

extraordinary, unique, unusual

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Practice OWAD in a conversation:

"He drives a PLAIN-JANE car, but with the most amazing sound system."