Trump’s plan for the US to restart testing of nuclear weapons is nuts and shows that he’s thinking with his testicles rather than his brains. Nuclear, formed from nucleus in reference to the splitting of the nucleus of the atom, comes from Latin nucleus “kernel” from nucula “little nut”, the diminutive of nux “nut”, which can be traced back to the Proto-Indo-European *knuk-, an extended zero-grade form of the root *kneu- “nut”, which also had the extended zero-grade form *knud- which produced the Proto-Germanic root *hnut- leading to Old English hnutu “nut” and Modern English nut. Since nuts were considered a special treat the plural nuts gained the sense “any source of pleasure or delight” in the 17th c., and in the 18th c. the expression be nuts on meant “be very fond of”, and by the 19th c. nuts came to mean “crazy”. The slang sense of nuts meaning “testicles” first appears by 1915.

As for the word testicle itself, it comes from Latin testiculus, a diminutive of testis “testicle”, whose origin is debated, either from another Latin word testis meaning “witness” (source of the English word testify), from the notion that testicles bear witness to male virility, or it might instead be a figurative sense coming from the Latin word testa “pot, shell” — compare for instance French tête “head” which also comes from Latin testa. In Medieval Latin, testum “earthen pot” referred to an earthen vessel, also known as a cupel, in which the purity of a metal was ascertained by exposing it to high temperatures, and by analogy came the English word test by which a teacher may ascertain a student’s knowledge.