Tawasu (توسع) literally means to make something wide, or to extend it. In the context of Arabic grammar, it refers to leaving a sentence intentionally ambiguous or open so that its interpretation can encompass a broader meaning. The most famous dua known to Muslims is a perfect example of this concept:
هْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ
“Guide us the straight path”
In a context like this, you’d expect the word “to” to appear in the middle, but you’ll notice that it’s oddly omitted. هْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ literally means “guide us the straight path”, not “guide us to the straight path,” which would require the word إلى preceding it.
From his mercy, Allah purposely leaves this dua open-ended, making it broader and more inclusive. The dua isn’t only asking for guidance to the straight path, but guidance on it, once we get there. It’s comparable to a fill in the blank where multiple positive meanings apply.
Further, Allah SWT says in Surah Araf:
وَرَحْمَتِي وَسِعَتْ كُلَّ شَيْءٍ
“And my mercy extends over all things”
The word wasi’at (وَسِعَتْ) has the same root as the grammatical term Tawasu (توسع), both relating to the idea of expansiveness. In this case, Allah demonstrates the expansiveness of his mercy by making the dua expansive as well. It makes perfect sense that the scope of our duas is vast just as the mercy of the one we’re calling on is also vast.
Even more amazingly, this rhetorical broadening of Allah’s mercy is by itself an instantaneous reply to the dua for guidance found in the Ayah.