purr

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The soft vibrant sound made by a cat.
2. n. A sound similar to that made by a cat: the purr of an engine.
3. v. To make or utter a soft vibrant sound: The cat purred. The sewing machine purred.
4. v. To express by a soft vibrant sound.

Century Dictionary and Cyclopedia

1. To utter a low murmuring sound expressive of satisfaction or pleasure, as a cat. The sound is made by throwing the vocal cords into vibration measured and regulated by the respiration; and this vibration is strong enough to make the whole larynx tremble, so that it may be felt or seen from the outside. Purring is highly characteristic of the cat tribe, though probably not confined to it.
2. To express or signify by purring.
3. n. The sound made by a cat in purring.
4. n. See pur.
5. n. A sandpiper, Tringa alpina, commonly called dunlin.
6. n. A bivalve of the family Veneridæ, Tapes decussata. It inhabits chiefly the European coasts on sandy or gravelly bottoms between tide-marks. It burrows in the ground, and is usually indicated by two little holes about an inch apart, made by the siphons. The purrs are held in some esteem for food, being considered better than cockles. Also called butter-fish.

Wiktionary

1. v. Of a cat, to make a vibrating sound in its throat when contented.
2. n. The vibrating sound made by a cat in its throat when contented.

GNU Webster's 1913

1. v. To murmur as a cat. See pur.
2. n. The low murmuring sound made by a cat; pur. See pur.

WordNet 3.0

1. v. indicate pleasure by purring; characteristic of cats
2. v. make a soft swishing sound
3. n. a low vibrating sound typical of a contented cat