Before a friend of this descriptión
Shall lose a hair through Bassanio's fault.
Thus they came under the 'alias' rule, and what is now the penultimate vowel is long unless it be i. Examples are 'nation', 'accretion', 'emotion', 'solution', while i is shortened in 'petition', 'munition', and the like, and left short in 'admonition' and others. In military use an exception is made by 'ration', but the pronunciation is confined to one sense of the word, and is new at that. I remember old soldiers of George III who spoke of 'rātions'. Perhaps the ugly change is due to French influence.
Originally the adjectives from these words must have lengthened the fourth vowel from the end long, as nātĭŏnal, but when ti became sh they came to follow the rule of Latin trisyllables in our pronunciation.
Stems in -ic. Of these words we have a good many, both Latin and Greek. Those that came direct keep the stress on the vowel which was antepenultimate and is in English penultimate, and this vowel is short whatever its original quantity. Examples are 'aquatic', 'italic', 'Germanic'. Words that came through French threw the stress back, as 'lúnatic'. Skeat says that 'fanatic' came through French, but he can hardly be right, for the pronunciation 'fánatic' is barely three score years old. There is no inverted stress in Milton's
Fanátic Egypt and her priests.
As for 'unique' it is a modern borrowing from French, and of late 'ántique' or 'ántic', as Shakespeare has it, has followed in one of its senses the French use. It is a pity in face of Milton's
With mask and ántique Pageantry,
and it obscures the etymological identity of 'antique' and 'antic', but the old pronunciation is irredeemable. At least the new avoids the homophonic inconvenience.