سنسن 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.

• سِنْسِنٌ

  سِنْسِنٌ ذ The edge (S, M, L, K) of a vertebra (S, M, L) or of the vertebræ (K) of the back; (S, M, L, K;) as also and : (M, L, K:) pl. سَنَاسِنُ: (S, L:) and the head [of any] of the bones of the breast: and the extremi…

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