一头 (yì tóu): All of a sudden / from the very beginning (Noun, Adverb) — Meaning & Stroke Order

Why did you conclude all of a sudden that this plan is not feasible?

He did not accept the other party's proposal all of a sudden; instead, he thought carefully.

An elephant is drinking water by the river.

He rushed into the rain all of a sudden but immediately turned back because he forgot his umbrella.