An adverb meaning 'at the same time' or 'simultaneously'; used when two or more actions or events occur together.
彼は電話をかけながら、同時にメールも読んでいた。
He was reading emails at the same time as making a phone call.
地震と津波が同時に発生した。
An earthquake and a tsunami occurred at the same time.
三つのボタンを同時に押してください。
Please press the three buttons at the same time.
A conjunction used in the pattern '...と同時に' meaning 'just as...' or 'the moment when...' indicating that one event happens exactly when another occurs.
ドアが開くと同時に、彼女は部屋に飛び込んだ。
Just as the door opened, she rushed into the room.
時計が正午を示すと同時に、花火が打ち上げられた。
At the moment the clock struck noon, fireworks were launched.
彼が部屋に入ってくると同時に、電話が鳴った。
The phone rang the moment he entered the room.
A conjunction meaning 'at the same time' in the sense of 'on the other hand' or 'as well as' used to present a contrasting or additional point.
彼の提案は面白い。同時に、実現には多くの課題がある。
His proposal is interesting. At the same time, there are many challenges to realizing it.
新技術は便利だが、同時に失業を生む可能性もある。
New technology is convenient, but at the same time it can also create unemployment.
その計画は安価である。同時に、品質に問題がある。
The plan is inexpensive; at the same time, there are quality issues.