The introduction of the word "index" into English from the Latin word in the nominative shows that it dates from a comparatively recent period, and came into the language through literature and not through speech. In earlier times it was the custom to derive our words from the Latin accusative. The Italian word indice was from the accusative, and this word was used by Ben Jonson when he wrote, "too much talking is ever the indice of a fool" (Discoveries, ed. 1640, p. 93). The French word indice has a different meaning from the Italian indice, and according to Littré is not derived from index, but from indicium. It is possible that Jonson's "indice" is the French, and not the Italian, word.
Drayton uses "index" as an indicator:
"Lest when my lisping guiltie tongue should hault,
My lookes might prove the index to my fault."
—Rosamond's Epistle, lines 103-104.
Shakespeare uses the word as a table of contents at the beginning of a book rather than as an alphabetical list at the end: for instance, Nestor says:
"Our imputation shall be oddly poised
In this wild action: for the success,
Although particular, shall give a scantling
Of good or bad unto the general;
And in such indexes, although small pricks
To their subsequent volumes, there is seen
The baby figure of the giant mass
Of things to come at large."
—Troilus and Cressida, I. 3.
Buckingham threatens:
"I'll sort occasion,
As index to the story we late talk'd of,
To part the queen's proud kindred from the king."
—Richard III., II. 2.
And Iago refers to "an index and obscure prologue to the history of lust and foul thoughts" (Othello, II. 1). It may be remarked in the quotation from Troilus and Cressida that Shakespeare uses the proper plural—"indexes"—instead of "indices," which even now some writers insist on using. No word can be considered as thoroughly naturalised that is allowed to take the plural form of the language from which it is obtained. The same remark applies to the word "appendix," the plural of which some write as "appendices" instead of "appendixes." In the case of "indices," this word is correctly appropriated to another use.
Indexes need not necessarily be dry; and some of the old ones are full of quaint touches which make them by no means the least interesting portion of the books they adorn. John Florio's translation of Montaigne's Essays contains "An Index or Table directing to many of the principal matters and personages mentioned in this Booke," which is full of curious entries and odd cross references. The entries are not in perfect alphabetical order. A few of the headings will give a good idea of the whole:
"Action better than speach."
"Action to some is rest."
"Beasts are Physitians, Logitians, Musitians, Artists, Students, Politikes, Docible, Capable of Military Order, of Affections, of Justice, of Friendship, of Husbandry, of thankefulnesse and of compassion," etc.
"Bookes and Bookishnesse."
"Bookes not so profitable as Conference—as deare as children."
"Bruit creatures have imagination."
"Cloysters not without cares."
"Good fortune not to be despised altogether."
"Societie of bookes."