Kilts that aren't pleated?

[NewGuise]

What does the OED mean by petticoat in this context? I "knew" it to be a feminine garment.

Sorry. I should have noted that a "petticoat" ("petty" meaning secondary or subordinate as in "petty officer") was originally an undergarment for men or women. For men, early on, it was a padded garment, worn over the shirt but under a doublet. Later the term could mean "waistcoat."

But yes, the line between 'masculine' and 'feminine' garments is both thin and moveable, across culture and across time. Boys even in Victorian England, much as in Shakespeare's day, often wore clothing resembling a girl's dress until they were 6 or 7, after which they were "breeched."