the larva of a butterfly or moth
First attested in the mid-15th century, the noun caterpillar is probably from catepeluse and variants, which were the Anglo-Norman forms of the Old French feminine noun chatepelose and variants, meaning literally hairy she-cat. In his textbook Lesclarcissement de la langue francoyse (1530), the teacher and scholar of languages John Palsgrave wrote:
Caterpyllarworme — chattepellevse.
(The French name for caterpillar is now the feminine noun chenille, from Latin canicula, small she-dog, diminutive of canis, dog, either from the hairy appearance of the larva or from the shape of its head.)
According to Ernest Adams in On the names of caterpillers, snails, and slugs (Transactions of the Philological Society – 1860), the giving to hairy caterpillars of a French name derived from the cat is paralleled in Lombard Italian by the feminine nouns gatta, she-cat, and gattola, she-kitten, and in Swiss German by Teufels-katz, Devils-cat.
Similarly, in several languages, the catkin is named from its soft downy appearance. The English noun catkin is a rendering of obsolete Dutch katteken (diminutive of obsolete katte, cat), meaning kitten and applied to the downy inflorescence. The French masculine chaton (diminutive of masculine chat, cat) and the German neuter Kätzchen (diminutive of feminine Katze, cat) have the same meanings.
Dialectal names for hairy caterpillars were woubit and variants, the first element of which means wool and the second element apparently means insect. The adjective hairy was prefixed to these names once they had ceased to be descriptive and significant.
The final hissing sound of catepeluse might have been treated in English as a plural formative, and the supposed singular would have been readily associated with the word piller, meaning pillager, plunderer. This is illustrated by the fact that in a large number of parallel passages, piller and caterpiller were used synonymously. In The practise of papisticall Prelates (1530), the English translator and Protestant martyr William Tyndale (circa 1494-1536) wrote:
Assoone as the Monkes were fallē, then sprang these begging Fryers out of hell, the last kynde of Caterpillers, in a more vile apparell, and a more straite religion, that (if ought of reliefe were left among the laye men for the poore people) these horseleches might sucke that also. Which dronebees as soone as they had learued their crafte, and had buylt them goodly and costly nestes, and their limiters had denided all countryes amōg them to begge in, and had prepared liuinges of a certain tie, though with begging, then they also tooke dispeusations of the Pope for to liue as largely and as lewdly as the Monkes.
And yet vnto the laye men whome they haue thus falsely robbed, and frō which they haue deuided themselues, and made them a seuerall kyngdome among themselnes, they leaue the paying of tolle, custome, and tribute (for vnto all yᵗ charges of the realmes will they not pay one mite, and the finding of all the poore, the finding of scholers for the most part, the finding of these foresayd horseleches, and caterpillers, the begging Fryers, the repayring of the hye wayes, and bridges, the building and reparations of their Abbaies and Cathedrall Churches, Chapels, Coledges, for which they sende out their pardons dayly by heapes, and gather a thousand pounde for euery hundred that they bestow truely).
Thus influenced by piller, the regular earlier ending was -er. The alteration caterpillar (perhaps after pillar), occasional in the 17th century, was adopted by the English lexicographer Samuel Johnson (1709-84) in A Dictionary of the English Language (1755) and has since prevailed.
The noun caterpillar has been applied to an endless track, driven by sprockets or wheels, used to propel a heavy vehicle and enable it to cross soft or uneven ground; it also denotes a vehicle, such as a tractor, tank or bulldozer, driven by such tracks. (Caterpillar is a proprietary term in this sense). A caterpillar tractor is called in French un tracteur à chenilles, the noun chenille, calqued on English caterpillar, denoting each of the endless tracks.