"loose metal ball serving as the clapper of a sleigh-bell," 1875, diminutive of jingle (n.).
Entries linking to jinglet
jingle n.
"tinkling or clinging sound," such as made by small bells, 1590s, from jingle (v.). Meaning "something that jingles" is from 1610s, especially "metallic disc on a tambourine." Meaning "song in an advertisement" first attested 1930, from earlier sense of "catchy array of words in prose or verse" (1640s).