«عَلَيَّ عَشَرَةُ دَرَاهِمَ وَنَيِّفٌ»
“I owe ten dirhams and an additional amount.”
Nayyif indicates a surplus, but the size of the surplus is unspecified. If the speaker clarifies that the surplus is one dirham, the previously concealed quantity becomes determinate.
The first ten dirhams were known from the outset; only the extra portion needed explanation. Tafsir makes the whole acknowledged amount calculable. It also illustrates that one part of a statement may be clear while another part remains ambiguous.