Tawakkul:
Allah speaks about the concept of reliance and trust in around 70 verses of the Qur’an, each using a verb or noun from the root و ك ل, which connotes entrusting your affairs to someone else – the same root as the word tawakkul. Allah says, for example, in Surah Aal-’Imraan, verse 159,
فَإِذَا عَزَمْتَ فَتَوَكَّلْ عَلَى ٱللَّهِ ۚ إِنَّ ٱللَّهَ يُحِبُّ ٱلْمُتَوَكِّلِينَ
Once you make a decision, put your trust (فَتَوَكَّلْ) in Allah. Surely Allah loves those who trust in Him.
Surah Ghafir (verse 44) is one instance, though, in which Allah uses the word أُفَوِّضُ from the root ف و ض, to convey what – according to the translation – appears to be the same meaning,
فَسَتَذْكُرُونَ مَآ أَقُولُ لَكُمْ ۚ وَأُفَوِّضُ أَمْرِىٓ إِلَى ٱللَّهِ ۚ
And you will remember what I say to you, and I entrust (أُفَوِّضُ) my affair to Allāh. Indeed, Allāh is Seeing of [His] servants.”
Tawakkul is once you have taken steps to fulfill a matter, you then entrust your affairs to Allah with reliance. Tafweed (which is the noun corresponding to the verb أُفَوِّضُ) is when you have no ability to do anything about the matter, and so you entrust it to Allah with submission.
Thus, one first submits their affairs to Allaah (أُفَوِّضُ), after which he would take measures towards achieving his goal, and then place his reliance upon Allah for the outcome (tawakkul).
The reason for Allah using the word أُفَوِّضُ in this single instance in Surah Ghaafir becomes clear once we realise that the person talking is the believing man from the family of Fir’awn. He tried to warn Fir’awn against killing Musa (peace be upon him), but could not actually take any physical measures to prevent it, other than talk about it. Thus, his reliance could most precisely only be described as one of tafweed and not tawakkul.