مجس doesn't appear in Hans Wehr's Modern Standard Arabic dictionary, but Lane's Arabic-English Lexicon has an entry for it. Select the entry below for the full classical Arabic definition.

• مَجَسٌّ

  مَجَسٌّ مجس (A, TA) and ↓مَجَسَّةٌ (S, A, Mgh, Msb, K) The place which one feels with his hand, (A,* Mgh, K, TA,) for the purpose of testing it, that he may form a judgment of it: (Mgh:) and ↓ the latter, the place which…

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