Abrupt, Unexpected, Sudden
noun, な adjective
A sudden stab is abrupt and unexpected. Quick, dodge!! 唐突 describes sudden actions or events that catch people off guard.
とうとつ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
彼女、唐突に車の修理をしてほしいって俺に頼んできたんだよ。
She suddenly asked me to repair her car.