backの定義

• 0 to the place where someone or something was before -- 元に（へ）, （元の位置に）戻って

  • I put it back in the cupboard.

  • When do you go back to college?

• 1 as a reply or reaction to something -- 折り返し, 反応して

  • Can I call you back later?

• 2 in a direction behind you -- 後ろへ（に）, 後方へ（に）

  • She stepped back.

• 3 to the state something or someone was in before -- （元の状態に）戻って

  • Try to go back to sleep.

• 4 to an earlier time -- 過去に, （時間を）さかのぼり

  • I heard from them back in January.

  • Looking back, I think we did the right thing.

• 5 in one direction then the opposite way, many times -- 行ったり来たり, 前後に

  • She goes back and forth between London and Paris quite often.