رهو 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.

• رَهَا Form 1

  1 رَهَا بَيْنَ رِجْلَيْهِ ذ , aor. يَرْهُو, (AO, JK, S,) inf. n. رَهْوٌ, (AO, S, K,) He parted, or made an opening between, his legs: (AO, S, K:) or he parted widely, or made a wide opening between, his legs. (JK.) Hence…

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• رَهْوٌ

  رَهْوٌ ذ inf. n. of 1. (S, K, &c.) -b2- Also An intervening space (JK, TA) between two things, (JK,) as, for instance, between the two humps of a camel of the species termed فَالِج. (TA.) -b3- A place where water remains…

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