na-adjective, noun
Describes an action or change that happens without warning or preparation. Often used in formal or written contexts.
彼の卒爾な態度に驚いた。
I was surprised by his abrupt attitude.
卒爾な質問で失礼します。
I apologize for the sudden question.
突然 is the common, everyday word for 'sudden'. 卒爾 is more formal and literary, often implying a lack of preparation or abruptness in behavior.
The exact derivation is uncertain; the kanji 卒 and 爾 are used phonetically to represent the sound 'そつじ', which may be related to older Chinese-derived terms for abruptness.