OED indicates that the term appears in English language only in the late 19th century:

loan-word n. [= German lehnwort] a word adopted or borrowed from another language.

1874 A. H. Sayce Princ. Compar. Philol. v. 171 Loan-words are common to all dialects.

1900 Margoliouth in Expositor Apr. 248 Isaiah's oracles were full of Aramaic loan-words.

But, if you refer to the term in a broader sense, I think genomics and philology can give us clues. All human words derive from a primitive language originated in Africa about 200K years ago.

Ruhlen, M. (1994). On the origin of languages : studies in linguistic taxonomy. Stanford, Calif.: Stanford University Press.

English has become the lingua franca of the world in the fields of business, science, aviation, computing, Education,  politics and entertainment. The English lexicon includes words borrowed from an estimated 120 different languages.  Although a huge number of words have been imported into English from other languages over the history of its development, many English words have been Incorporated  into foreign.Languages in a kind of reverse adoption process.  Anglicism such as stop, sport, tennis, golf, weekend,  jeans, bar, airport, hotel, etc  are among  the most universally used in the World. After centuries of acquisition, borrowing and adaptation, English has ended up with a vocabulary second to none in its richness and breadth, allowing for the most diverse shadings of  meaning. The latest full revision of the “Oxford English Dictionary”, published in 1989 and considered the premier dictionary of the English language, contains about  615,000 word entries, listed under about 300,000 main entries. This include some scientific terms, dialect words and slang, but does not include more specialized scientific and technical terms, nor the large number of more recent neologisms coined each passing year. "Webster's Third New International Dictionary”, published in1961, lists 475,000 main headwords. Philip Dur kin's Monographs deals with loan words, thousands of which have been absorbed into English ever since thefifth century A.D. up to the  present day.