👉 Okay, let’s tackle this rather… prickly little piece of linguistic weirdness. You stumbled upon, frankly, a seriously obscure and somewhat aggressively antiquated bit of 19th-century English slang.
What exactly is a "Nilghau”?
Essentially, a "nilghau, nilghaw, or nilgaw," as the old boys in the Victorian age were calling it, was a derogatory, almost obscene, name for a young woman who was considered hysterical and therefore, essentially, a bit mad. (And, let's be brutally frank, of very little account socially). Think early days of the hysterical female hysteria panic—the kind where women suffering from this supposed condition would often faint dramatically in public to prove their malady.
Now, here's what makes it fascinatingly awful: It comes from a rather unfortunate and frankly, quite insulting, reference. The word originates from the now-extinct Bhutanese blue poppy ( Æ., ǂ —, Ǧ). These poppies were historically used in a very specific and potent kind of hallucinogenic tea.
Essentially, being called a nilghau meant that you were essentially as delusional, erratic, and frankly, out of your head, as someone who'd just spent the night steeped in that poppy draught. The name was a way to immediately discredit her with a rather pointedly unpleasant nickname. It’s basically saying "You are as mad as a blue