dangerous; perilous; threatening; stormy; volatile; tense; critical; serious
stern (expression); hostile (attitude); sharp; harsh
会議の空気は険悪になった。
The atmosphere in the meeting became tense.
両国の関係は険悪な状態に陥った。
The relations between the two countries fell into a tense state.
台風が近づき、空模様が険悪になってきた。
As the typhoon approached, the sky started to look threatening.