This belongs to the category of “wow, I never knew”. The word spurious in common usage means false or fake. The word comes from Latin spurius meaning illegitimate as in illegitimate child, a bastard. This was its original use in English, later becoming to refer to anything that is not quite genuine. Like the word genuine itself, there must be an enormous number of words a phrases related to birth. Genuine goes back to the P-IE *gene- root referring to birth. Genuine, gender, gene, generation, genetics, even genius and many others, and in a roundabout way even the word kin. And then there are words born of Latin natus (born). There is native, natural, natal, nativity, even natural and so many others with the same heritage.
In Kentucky, you will often hear of someone feeling puny. Commonly, the word puny means small or insignificant. In colloquial Kentuckian, it means sick, or slightly unwell. Puny also is a birth word. Puny is an anglicized French puisne or puis (after) ne (born) that is, a child born after another child. That is, a lesser child. How this comes to mean not feeling well, is well, I am not sure, although I have used it myself and rather like it.
Two Strikes 