يرنأ doesn't appear in Hans Wehr's Modern Standard Arabic dictionary, but Lane's Arabic-English Lexicon has 2 entries for it, distinguished by diacritics. Select one below for the full classical Arabic definition.

• يَرْنَأَ Form Q. 1

  Q. 1 يَرْنَأَ لِحْيَتَهُ ذ (K, TA; in the CK, [erroneously,] تَرَنَّأَ;) He dyed his beard with يرنّأ. (K.) A strange verb as to its form, (K,) which [except in its final vowel] is that of an aorist, though it is a prete…

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• يُرَنَّأٌ

  يُرَنَّأٌ ذ (S, K) and يَرَنَّأٌ and يُرَنَّآءٌ (K) and يُرَنَّا (without ء) and (accord. to [the Bári', as mentioned in] the TA, art. رنأ,) يَرْنَأٌ and يُرْنَأٌ and (accord. to MF, who omits the two forms here immedia…

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