reward (from God)
Masculine verbal noun (maṣdar) of ثَابَ (to return). The concept is that reward 'returns' to the doer of good. Related: مَثُوبَةٌ (reward), ثَوْبٌ (garment - different meaning, same root).
Thawāb motivates good deeds in Islam. The Quran promises both worldly and otherworldly rewards, with the reward of the Hereafter being far superior and eternal.