also: ひょうちゅう
icicle
The common word for an icicle, a hanging spike of ice formed by dripping water that freezes.
A long icicle is hanging from the eaves.
ice pillar (for cooling a room)
Only when written 氷柱 · Only with reading ひょうちゅう
A pillar-shaped block of ice used historically to cool a room. This sense is restricted to the reading ひょうちゅう and is rare in modern usage.
Only with reading つらら
Archaic meaning for つらら, simply 'ice'. Not used in modern Japanese; the standard word for ice is 氷 (こおり).
暖かくなってつららが落ち始めた。
It got warmer and icicles started falling.
In old houses, people placed an ice pillar in the room to keep cool in summer.
In old language, つらら could simply mean 'ice'.
The word is usually written in kana. The kanji spelling 氷柱 is also used, especially in literary or formal contexts.
Kanji spelling for つらら. Can also be read ひょうちゅう, but that reading is restricted to the ice pillar sense.
Reading ひょうちゅう is used only for the ice pillar sense (sense 2). Rare in modern Japanese.
Rare kanji spelling for つらら. The character 氷 alone usually means 'ice' and is read こおり.
The word つらら is of native Japanese origin. The kanji 氷柱 literally mean 'ice pillar', which matches the icicle meaning. The reading ひょうちゅう is the on'yomi of these characters.