Tawheed- the oneness of Allah. The entire faith is based off of this. This is probably the most important concept in Islam.

Tawheed is the belief in the Oneness of God, and is the most important concept of Islam. It is an Arabic word that comes from the root letters "whd," which is the same root for the number one in Arabic (Wahid) The three types of Tawheed are: Tawheed ar-Rububiyyah-- Oneness of Lordship Tawheed al-Uluhiyyah-- Oneness of Worship Tawheed al-Asma was-Siffat-- Oneness of Attributes

The Arabic term for believing in one god is "Tawhid". It refers to the concept of monotheism, the belief in the oneness of God in Islam.

Another word for oneness is?

The Farsi word for 'oneness' is یکی‌پاره (Yekipareh).