Ez-Zann is interpreted in three ways:
1. Ez-Zann is used in the sense of yaqīn (certain knowledge); as in the following verses:
David thought that We had only tested him (that is, David certainly / definitely realized that We had made it a trial for him). (Ṣād 38:24)
Indeed, I was certain that I would be meeting my account (that is, I knew / believed with certainty). (al-Ḥāqqa 69:20) If they are certain (yaqīn) that they will uphold the limits of Allah... (al-Baqara 2:230)
2. Ez-Zann is used in the sense of shakk (doubt); as in the following verse:
You said, "We do not know what the Hour is; we think it is nothing but conjecture (that is, we doubt it), and we are not convinced with certainty." (al-Jāthiya 45:32)
3. Ez-Zann is used in the sense of accusation (tuhma); as in the following verses:
He is not accused (under suspicion) regarding the unseen. (al-Takwīr 81:24)
You were thinking ill thoughts about Allah, (that is, you were accusing the Prophet (peace and blessings be upon him) regarding the news Allah gave about your victory). (al-Aḥzāb 33:10)