Meaning

noun a rapid series of short loud sounds (as might be heard with a stethoscope in some types of respiratory disorders)

noun a baby's toy that makes percussive noises when shaken

noun loosely connected horny sections at the end of a rattlesnake's tail

originFrom Middle English ratelen, of uncertain origin; perhaps borrowed from Middle Dutch ratelen or of native origin related to Old English hratele, hrætele (“a plant known for its rustling or rattling sound”), ultimately imitative. The noun (c. 1500) is from the verb.

Etymology from Wiktionary, CC BY-SA 3.0