Tafsir of Al-Qamar 54:16

This is an interrogative for the purpose of magnification and astonishment. It means: "They were of a tremendous nature that description cannot encompass."

Al-Nudhuri (my warnings) is a verbal noun, similar to al-indhar (warning). It has been said that it is the plural of nadhir in the sense of indhar (warning). Some have considered it to mean "that which is warned against," but this holds no weight, and the same applies to considering it to mean "the warner."

It is possible that the verb kana (was) is deficient (naqisah), in which case kayfa (how) occupies the position of the predicate. It is also possible that it is complete (tammah), in which case kayfa occupies the position of the adverbial state (hal).