This is the 4168th most frequent Japanese word.
一同
"All present" or "everyone together."
The word 一同 is used to denote 'all members of a group,' specifically the employees in this context.
社員一同がお客様に感謝を伝えます。
All employees express their gratitude to the customers.
The word 一同 is used here to mean 'all members of a friend group.'
友人一同が結婚式に参加しました。
All the friends attended the wedding.
The word 一同 refers to 'the collective group of the class' within this sentence.