pistons is a form of:

Caterpillar



noun
1.
(the larva of a butterfly or moth. The caterpillar spins a cocoon or chrysalis from which it comes out as a fully developed insect with wings) ដង្កូវមេអំបៅ, ច្រវ៉ាក់រថក្រោះឬត្រាក់ទ័រ, caterpilla tractor ត្រាក់ទ័រកង់ច្រវ៉ាក់
ENGLISH MEANING
noun
1.
The larval state of a butterfly or any lepidopterous insect; sometimes, but less commonly, the larval state of other insects, as the sawflies, which are also called false caterpillars. The true caterpillars have three pairs of true legs, and several pairs of abdominal fleshy legs (prolegs) armed with hooks. Some are hairy, others naked. They usually feed on leaves, fruit, and succulent vegetables, being often very destructive, Many of them are popularly called worms, as the cutworm, cankerworm, army worm, cotton worm, silkworm.
2.
A plant of the genus Scorpiurus, with pods resembling caterpillars.