形容词突然英文表达方式是 "sudden"。
"Sudden" 源自拉丁文 "subitus"，意思是 "suddenly, without warning"。
例句：
The sudden thunderstorm caught us off guard. (突然的雷暴让我们措手不及。)
The sudden change in temperature made me shiver. (气温的突然变化让我发抖。)
She had a sudden reapzation that she had forgotten her keys. (她突然意识到她忘记了钥匙。)