Is it farther or further?
(plural testes), 1704, from Latin testis "testicle," usually regarded as a special application of testis "witness" (see testament), presumably because it "bears witness" to virility (cf. Greek parastates, literally "one that stands by;" and French slang témoins, literally "witnesses"). But Buck thinks Greek parastatai "testicles" has been wrongly associated with the legal sense of parastates "supporter, defender" and suggests instead parastatai in the sense of twin "supporting pillars, props of a mast," etc. Walde, meanwhile, suggests a connection between testis and testa "pot, shell, etc."
testis tes·tis (těs'tĭs)
n. pl. tes·tes (-tēz)
The male reproductive gland, the source of spermatozoa and the androgens, normally occurring paired in an external scrotum. Also called didymus, orchis.