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riding habit

n. A woman's garment for horseback riding.

WordNet
riding habit

n. habit for riding horses

Wikipedia
Riding habit

A riding habit is women's clothing for horseback riding.

Since the mid-17th century, a formal habit for riding sidesaddle usually consisted of:

Low-heeled boots, gloves, and often a necktie or stock complete the ensemble. Typically, throughout the period the riding habit used details from male dress, whether large turned cuffs, gold trims or buttons. The colours were very often darker and more masculine than those on normal clothes. Earlier styles can be similar to the dresses worn by boys before breeching in these respects.

When high waists were the fashion, from roughly 1790 to 1820, the habit could be a coat dress called a riding coat (borrowed in French as redingote) or a petticoat with a short jacket (often longer in back than in front).