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Is there any further implication to be gleaned from this and how did this meaning come to be? Is there any suggestion that the male genitals are somehow an obstacle to enlightenment?

marked as duplicate by cypher, Dono, Earthliŋ, snailboat Feb 6 '15 at 23:40

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Excerpt from 日本国語大辞典 entry:

まら 【魔羅・摩羅】

(1)「ま(魔)(1)」に同じ。

*却癈忘記〔1235〕下「勤行之人の魔道に堕ると、世間に人のいふ事、甚謂有事也。魔と者具には魔羅と云ふ」

(2)((1)から転じたとも、排泄する意の「まる」の交替形ともいう)陰茎をいう。もと僧侶が用いた語。

*霊異記〔810〜824〕中・一一「卒爾に𨳯(マラ)に蟻著きて嚼み〈国会図書館本訓釈 𨳯 万良〉」

That means, the "penis" sense may have come from buddhist māra, or the verb まる "excrete", or confusion between both.

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