Testicle

google

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late Middle English: from Latin testiculus, diminutive of testis ‘a witness’ (i.e. to virility).

wiktionary

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Borrowed from Latin testiculus, diminutive of testis.

etymonline

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testicle (n.)

early 15c., alteration of testicule (late 14c.), from Latin testiculus, diminutive of testis "testicle" (see testis). Old English had beallucas (see ballocks) and herþan, probably originally "leather bag" (compare heorþa "deer-skin"). The commonest slang terms for them in other languages are words that mean "balls," "stones," "nuts," "eggs."