Sonnet
2 of the 7 encyclopedias on this shelf carry an entry for Sonnet. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a lyric poem dealing with some single idea, or single phase of sentiment expressed in a single stanza of prescribed form. The sonnet originated with Petrarch, an Italian poet of the fourteenth century. The first sonnets in the English language were written by Thomas Wyatt, an English poet of the sixteenth century much employed by Henry VIII on foreign embassies. He had a friend and imitator in the poet Surrey. The sonnet consists of fourteen iambic pentameter lines. Milton's sonnet On His Blindness is a fine example of this form of poetry and will serve to show the usual arrangement of rhymes: When I consider how my light is spent a Ere half my days, in this dark world and wide, And that one talent which is death to hide b Lodged with me useless, though my soul more bent To serve therewith my Maker, and present a My true account, lest he returning, chide; b "Doth God exact day-labor, light denied?" b I fondly ask. But Patience, to prevent a That murmur, soon replies "God doth not need c Either man's work, or his own gifts. Who best Bear his mild yoke, they serve him best. His state Is kingly; thousands at his bidding speed, c And post o'er land and ocean without rest; d They also serve who only stand and wait. e Poets vary the arrangement of rhymes slightly, especially in the last six lines, where the order c d c d c d is very common. In a perfect sonnet, the emotional feeling or sentiment increases through the first eight lines, or octave as they are called, and subsides through the last six lines or sextet, reaching the climax in the eighth line. The sonnet has sometimes been called the "wave of flow and ebb." Shakespeare, Milton, Keats, Wordsworth, Mrs. Browning, and many other poets have written beautiful sonnets. Mrs. Browning's Sonnets from the Portuguese are among the finest examples. See Poetry ; Lyric ; Wyatt
Collier's New Encyclopedia (1921)
a species of poetic composition first brought into notice by Petrarch, and consisting properly of 14 iambic verses of 11 syllables. It is divided into two chief parts, each consisting of two divisions in the former, each comprising four lines (quatrain); in the latter, three (terzina). The quatrains have two rhymes, each of which is repeated four times; and in the common Italian form the rhymes are the first, fourth, fifth, and eighth verses, and the second, third, sixth, and seventh; but several other forms are also adopted. In the two terzine, there are either three rhymes each twice repeated, or two rhymes thrice repeated in all positions. The sonnet generally contains one principal idea pursued through the various antitheses of the different strophes, and adorned with the charm of rhyme. Italy and Spain are the countries in which the sonnet is most cultivated, the lightness and flexibility of their languages being eminently suited for such compositions.