since

The word since is used as a preposition to indicate a specific time in the past up to the present or to express a cause or reason for something.

• I have lived here since 2010. — 私は2010年からここに住んでいます。
• We haven't seen each other since last summer. — 私たちは昨夏以来会っていません。

Since is used as a conjunction to indicate the reason for something happening, similar in meaning to 'because'.

• I stayed home since it was raining. — 雨が降っていたので私は家にいました。
• He decided to leave early since he was feeling tired. — 彼は疲れていたので早く出発することにしました。

Since is used as an adverb to refer to the time from a specific point in the past up until now.

• I have been working here since then. — それ以来、ここで働いています。
• They have been friends since childhood. — 彼らは子供の頃から友達です。