石灰|せっかいsekkai[1]atamadaka (head-high)

1. no-adjectivelime; quicklime; caustic lime

• Synonym生石灰せいせっかいNeutralRefers specifically to calcium oxide made by heating limestone; it heats up when water is added. 「石灰」 is the umbrella term for quicklime and slaked lime.
• Related酸化カルシウムさんかカルシウムNeutralThe chemical name for 「生石灰」, with formula CaO; a chemistry term, rarely heard in everyday speech.

Use 「石灰」 for lime in general, including the kind used to mark lines on a field. For calcium oxide specifically say 「生石灰」; 「酸化カルシウム」 is its chemical name, mostly in chemistry contexts.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 生石灰きせっかい、消石灰しょうせっかいなどの総称そうしょう。