Wiktionary
n. (context Islam English) the central Islamic doctrine of the divine unity
Wikipedia
Tawhid ( , meaning the oneness [of God]"; also transliterated as Tawheed and Towheed) is the indivisible oneness concept of monotheism in Islam. Tawhid is the religion's most fundamental concept and holds that God ( Allah, literally Al-Ilāh "the God") is One () and Single (). Because of the "principle of Tawhid the Islamic belief in God is considered Unitarian."
Tawhid constitutes the foremost article of the Muslim profession of faith. The first part of the Shahada (the Islamic declaration of faith) is the declaration of belief in the oneness of God. To attribute divinity to a created entity, known as shirk, is an unpardonable sin according to the Qur'an. Muslims believe that the entirety of the Islamic teaching rests on the principle of Tawhid.
There is an uncompromising monotheism at the heart of the Islamic beliefs ( Aqidah) which is seen, from an Islamic standpoint, as distinguishing Islam from other major religions. However, Tawhid is analogous to the monotheistic concept of God in Judaism as declared in the Shema (the Jewish declaration of faith), and is also analogous to Christian Unitarianism adhered to by a minority of Christian denominations affirming the oneness and indivisibility of God in Christianity (in contrast to the "One God in Three Persons" Trinity of most Christian faiths).
The Qu'ran asserts the existence of a single and absolute truth that transcends the world; a unique, independent and indivisible being, who is independent of the entire creation. God, according to Islam, is a universal God, rather than a local, tribal, or parochial one—God is an absolute, who integrates all affirmative values and brooks no evil.
Islamic intellectual history can be understood as a gradual unfolding of the manner in which successive generations of believers have understood the meaning and implications of professing God's Unity. Islamic scholars have different approaches toward understanding it. Islamic theology, jurisprudence, philosophy, Sufism, even to some degree the Islamic understanding of natural sciences, all seek to explain at some level the principle of tawhid.
The classical definition of tawhid was limited to declaring or preferring belief in one God and the unity of God. Although the monotheistic definition has persisted into modern Arabic, it is now more generally used to connote "unification, union, combination, fusion; standardization, regularization; consolidation, amalgamation, merger;".