What caution applies to ikhtaṣartum and al-khaṣr?

Radd al-ʿAjz ʿalā al-Ṣadr: Repetition, Paronomasia and Derivation in Prose and Poetry

• Do not infer one root from surface resemblance
• Always treat them as one word
• Treat both as verbal nouns
• Classify them only as antithesis