Maybe the "the" in front of "kilt" is a sign of respect, similar to the usage "The Mackintosh"?
That's actually a reference to the Chief, who is the head of the clan, which is also a sign of respect, as you mentioned.

I've seen a lot of usage of the term "kilts" for a single garment from the 19th century, and even some older folks I know still use the plural "kilts" to describe a kilt.

But one improper use of terminology in this thread that I must correct: Men wear trousers, not "pants". Women wear pants.

Cheers,

Todd