>Whilst not in any dictionary, as far as I know...

oh, it's in the OED2, although it's listed as a "nonce word".

matriotism
nonce-wd. [Altered from patriotism, after L. mQter mother.]

Love of one's mother country or of one's ‘alma mater’.

1856 Lowell Lett. (1894) I. 301, I am delighted with your matriotism ‘Rome, Venice, Cambridge!’ 1885 H. C. Beeching in Academy 14 Feb. 109/2 Though Mr. Lang's matriotism is thus divided, he has only one fatherland.