The term "tawheed (or more appropriately, at-tawheed)" literally refers to "Islamic monotheism". It predates every other pillars of Islām. It is an umbrella housing various Islamic fundamental concepts including the concept of "al-īmān (belief)" and the articles of faith (ar-kānul-īmān).

At-tawheed as a fundamental islamic concept means the oneness of Allāh, the most High, in our acts of worship (`ibādāt) and every other exercises or acts that require having knowledge of His teachings, prohibitions or permissibles. Acts of worship (`ibādāt) includes solāh, zakāh, hajj etc. All these are dedicated to Him only.

The genesis of at-tawheed (Islamic monotheism) predates the creation of mankind. This, Allaah says:

كان ٱلنَّاسُ أُمَّةً وَٰحِدَةً فَبَعَثَ ٱللَّهُ ٱلنَّبِيِّۦنَ مُبَشِّرِينَ وَمُنذِرِينَ وَأَنزَلَ مَعَهُمُ ٱلْكِتَٰبَ بِٱلْحَقِّ لِيَحْكُمَ بَيْنَ ٱلنَّاسِ فِيمَا ٱخْتَلَفُوا۟ فِيهِۚ...

Meaning:

Mankind was [of] one religion [before their deviation]; then Allāh sent the prophets as bringers of good tidings and warners and sent down with them the Scripture in truth to judge between the people concerning that in which they differed... [Al-Baqarah 2:213]

The above verse implies and proves that the genesis of shirk (disbelief) came after the creation of man. In an Hadīth Qudsiy reported by Imām Muslim, Allāh the most High says:

خلقت عبادى حنفاء كلهم، وإنهم أتتهم الشياطين فاجتالتهم عن دينهم، وحرمت عليهم ما أحللت لهم، وأمرتهم أن يشركوا بى مالم أنزل به سلطانا

Meaning:

I have created My slaves as Hunafā' [having a natural inclination to worship Allah alone], and then the shayātīn (the devils) came to them and made them deviate from their deen, and they forbade them what I had permitted for them and commanded them to commit shirk [associating partners in worship] with Me for which I had never revealed any authority.

On the interval between the genesis of at-tawheed and ash-shirk, Ibn `Abbās (R.A) was reported to have said:

كان بين نوح وآدم عشرة قرون؛ كلهم على شريعة من الحق

Meaning:

The duration between Ādam and Nūh was ten centuries; for this period [before Nūh's time], all humans [existing as at that time] were all trailing on the path of truth [Islamic monotheism]

With the above, the genesis of shirk was said to have been dated back to the time of prophet Nuuh (peace be upon him).