مطر doesn't appear in Hans Wehr's Modern Standard Arabic dictionary, but Lane's Arabic-English Lexicon has 4 entries for it, distinguished by diacritics. Select one below for the full classical Arabic definition.

• مَطَرَتِ Form 1

  1 مَطَرَتِ السَّمَآءُ ذ , aor. مَطُرَ , inf. n. مَطَرٌ, [The sky, or, as it sometimes means, the rain,] rained; as also : (T, S, Msb:) but the former is said to relate to that which is sent in mercy, and the latter to t…

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• مُطِرٌّ

  مُطِرٌّ ذ A boy having a طُرَّة; as also : and the latter with ة is applied to a girl. (So in a copy of the A.) -b2- جَلَبٌ مُطِرٌّ (assumed tropical:) [A thing, or things, brought for the purpose of traffic,] come from …

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• مَطَرٌ

  مَطَرٌ ذ Rain: (A, Msb, K, TA:) pl. أَمْطَارٌ. (S, A, Msb, K.) See مَطْرَةٌ: and see also ظَهْرٌ, p. 1929, a.…

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• مَطِرٌ

  مَطِرٌ ذ : see مَاطِرٌ: -b2- and see also مَمْطُورٌ.…

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