complete incompatibility; like water and oil
A literary yojijukugo describing two people or things that are fundamentally incompatible, like water and fire or ice and hot coals. Rare in everyday speech; more common in written or formal contexts.
Those two are as incompatible as fire and water.
A common, everyday expression for incompatibility, literally 'water and oil'. 水火氷炭 is a much rarer, literary equivalent.
Another common idiom for a relationship of mutual hostility, like cats and dogs. 水火氷炭 emphasizes fundamental difference rather than active fighting.
A literary compound pairing 水 with 火 and 氷 with 炭, two conventional images of mutual incompatibility.