し始はじめる

し

は

じ

め

る

Meanings

1

ichidan verb, transitive verb

begin doing; start doing

Attaches to the continuative form (連用形) of a verb to express the beginning of an action. Used in everyday speech and writing.

雨あめが降ふり始はじめてから、急きゅうに寒さむくなった。

After it started raining, it suddenly got cold.

始はじめる
The standalone verb 'to begin (something)'; し始める is a compound auxiliary that attaches to other verbs to mean 'begin doing'.
出だす
Also means 'begin to' when used as an auxiliary (〜だす), but often implies a sudden or unexpected start, while し始める is more neutral.

Compound of the continuative form of する (し) + 始める (はじめる, 'to begin'). The し is the 連用形 of する, used here as a connector.