Intern
early 16th century (as an adjective in the sense ‘internal’): from French interne (adjective), interner (verb), from Latin internus ‘inward, internal’. Current senses date from the 19th century.
wiktionary
From French interner, from interne(“inner, internal”), from Latin internus(“within, internal”), compare Etymology 2
From French interne(“inner, internal”), from Latin internus(“within, internal”), from inter(“between”); compare etymology 1.
etymonline
intern (v.1)
1866, "to confine within set limits," from French interner "send to the interior, confine," from interne "inner, internal" (14c.), from Latin internus "within, internal" (see internal; also compare intern (n.)).
intern (n.)
"one working under supervision as part of professional training," originally "assistant resident physician, doctor in training in a hospital," 1879, American English, from French interne "assistant doctor," noun use of interne "internal," from Latin internus "within, inward" (see internal). Extended to other professions (originally teaching) from 1963 in reference to one under training and acquiring practical experience.
intern (v.2)
"to act or serve as as a (medical) intern," 1933, from intern (n.). Related: Interned; interning.
