だす
(Dasu)
Indicates the sudden or unexpected start of an action.
Connection rules
- +Verb (masu-stem) + だす
Examples
1.
今まで寝ていた赤ちゃんが急に泣きだした。

Ima made ne te i ta akachan ga kyuu ni naki dashi ta.
The baby who was sleeping until now suddenly started crying.
「Unexpected baby noise」
2.
五分前に急に雨が降りだしました。

Go fun mae ni kyuu ni ame ga furi dashi mashi ta.
It suddenly started raining five minutes ago.
「Sudden weather change」