Indicates being together with someone or sharing something; often appears as 'ともに' (together).
彼は妻と共に会社を立ち上げた。
He founded the company together with his wife.
困難な時期を共に乗り越えよう。
Let's overcome this difficult time together.
学生共に学び合う場を作りたい。
I want to create a place where students learn together.
Meaning 'same' — indicates that something is shared or identical, often used in compounds or phrases.
我々は目的を共にして行動した。
We acted sharing the same objective.
共通点が多く、考え方は共通している。
There are many common points; our ways of thinking are the same.
この二つの問題は背景が共であると言える。
You could say these two problems share the same background.
Used as a suffix meaning 'both/all/neither/none' (forms like '〜とも'); the word is usually written in kana.
二人とも約束の時間に来た。
Both of them came at the appointed time.
誰とも話さなかった。
I didn't talk to anyone.
一人とも欠けていないことを確認した。
I confirmed that not a single person was missing.
As a suffix ('〜とも'), used to refer to a group including the items mentioned (colloquial or somewhat old-fashioned in places); often written in kana.
親子共（とも）楽しめるイベントが開催される。
An event that parents and children can both enjoy will be held.
社員共（とも）で問題点を共有した。
All the employees together shared the issues.
村人共（とも）集まってお祭りを準備した。
The villagers together gathered to prepare the festival.