Having the characteristics or manners of a bumpkin; rustic, unsophisticated, or clumsy in a rural way.
From bumpkin (a clumsy, unsophisticated country person, likely from Dutch or Low German origins) plus -ly suffix forming adjectives. The word evolved in 16th-17th century English to describe rural behavior or appearance.
The suffix -ly can turn almost any noun into an adjective—this shows how flexible English is! 'Bumpkinly' emerged right when towns and cities were growing, so people needed a word to contrast rural folk with sophisticated city dwellers.
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