catrpillar - n.
1 a the larva of a butterfly or moth. b (in general use) any similar larva of various insects.
2 (Caterpillar) a (in full Caterpillar track or tread) propr. a steel band passing round the wheels of a tractor etc. for travel on rough ground. b a vehicle with these tracks, e.g. a tractor or tank. [perh. AF var. of OF chatepelose lit. hairy cat, infl. by obs. piller ravager]