1704, "kernel of a nut;" 1708, "head of a comet;" from Latin nucleus "kernel," from nucula "little nut," diminutive of nux (genitive nucis) "nut," from PIE *kneu- "nut" (source also of Middle Irish cnu, Welsh cneuen, Middle Breton knoen "nut," Old Norse hnot, Old English hnutu "nut").

The general sense of "central mass or thing, about which others cluster or matter collects," is from 1762. In biology, "dense, typically rounded structure in a cell, bounded by membranes," from 1831. Later they were found to contain the genetic material. Modern meaning in physics, "positively charged central core of an atom," is from 1912, by Ernest Rutherford, though theoretical use for "central point of an atom" is from 1844, in Faraday.

an alternative word for isotope, 1947, from nucleus + -ide.

"the representation of the undraped human figure in visual art," 1708, from French nud, obsolete variant of nu "naked, nude, bare," from Latin nudus (see nude (adj.)). In the nude "in a condition of being unclothed" is by 1856.

1530s, a legal term, "unsupported, not formally attested," from Latin nudus "naked, bare, unclothed, stripped," from PIE root *nogw- "naked" (see naked). General sense of "mere, plain, simple" is attested from 1550s. In reference to the human body, "unclothed, undraped," it is an artistic euphemism for naked, dating from 1610s (implied in nudity) but not in common use in this sense until mid-19c.

"complainer, nagger," 1960s, from Yiddish, from Slavic words meaning "fret, ache," related to the root of nudnik (q.v.).

"to push slightly with the elbow," 1670s, perhaps from Scandinavian (compare Norwegian nugge, nyggje "to jostle, rub;" Icelandic nugga "to rub, massage"). Figurative sense of "give a hint or signal to," as by a covert touch, is by 1831. Related: Nudged; nudging.

"a slight push with the elbow," 1787, from nudge (v.). Figurative sense of "a signal or hint intended to call attention, remind, etc." is by 1831.

word-forming element meaning "hairless; leafless; naked," from combining form of Latin nudus "naked, bare, stripped," from PIE root *nogw- "naked" (see naked).

type of mollusk having naked gills and no shell, 1844, literally "having naked gills," from nudi- "naked" + Latin branchae, from Greek brankhia "gills," plural of brankhion "fin."