A small whistle used to produce a sound, often for signaling or attracting attention.
When mountain climbing, it's reassuring to bring a whistle.
Standard kanji spelling.
Variant spelling without okurigana.
Compound of 呼び (yobi, 'calling', the continuative form of 呼ぶ yobu) and 子 (ko, 'small thing'). Literally 'calling device'.