The second, st (wise, wisest), is the current termination.
Of the English superlatives, the only ones that demand a detailed examination are those that are generally despatched without difficulty; viz., the words in most; such as midmost, foremost, &c. The current view is the one adopted by Rask in his Anglo-Saxon Grammar (§ 133), viz., that they are
compound words, formed from simple ones by the addition of the superlative term most. Grimm's view is opposed to this. In appreciating Grimm's view, we must bear in mind the phenomena of excess of expression; at the same time we must not depart from the current theory without duly considering the fact stated by Rask; which is, that we have in Icelandic the forms nærmeir, fjærmeir, &c., nearer, and farther, most unequivocally compounded of near and more, and of far and more.
Let especial notice be taken of the Mœso-Gothic forms fruma, first; aftuma, last; and of the Anglo-Saxon forms forma, aftema, aftermost; ufema, upmost; hindema, hindmost; midema, midmost; innema, inmost; ûtema, outmost; siðema, last; latema, last; niðema, nethermost. These account for the m.
Add to this, with an excess of expression, the letters st. This accounts for the whole form, as mid-m-ost, in-m-ost, &c. Such is Grimm's view.
Furthermost, innermost, hindermost.—Here there is a true addition of most, and an excess of inflection, a superlative form being added to a word in the comparative degree.
Former.—Here, as stated before, a comparative sign is added to a word in the superlative degree.
[§ 327]. The combination st occurs in other words besides those of the superlative degree; amongst others, in certain adverbs and prepositions, as among, amongst; while, whilst; between, betwixt.—Its power here has not been well explained.