isolated (adj.)

late 13c., ile, from Old French ile, earlier isle, from Latin insula "island," a word of uncertain origin.

Perhaps (as the Ancients guessed) from in salo "(that which is) in the (salty) sea," from ablative of salum "the open sea," related to sal "salt" (see salt (n.)). De Vaan finds this "theoretically possible as far as the phonetics go, but being 'in the sea' is not a very precise description of what an island is; furthermore, the Indo-Europeans seem to have indicated with 'island' mainly 'river islands.' ... Since no other etymology is obvious, it may well be a loanword from an unknown language." He proposes the same lost word as the source of Old Irish inis, Welsh ynys "island" and Greek nēsos "island." The -s- was restored first in French, then in English in the late 1500s.

"to set or place apart, to detach so as to make alone," by 1786, a back-formation from isolated (q.v.).

The translation of this work is well performed, excepting that fault from which few translations are wholly exempt, and which is daily tending to corrupt our language, the adoption of French expressions. We have here evasion for escape, twice or more times repeated; brigands very frequently; we have the unnecessary and foolish word isolate; and, if we mistake not, paralize, which at least has crept in through a similar channel. Translators cannot be too careful on this point, as it is a temptation to which they are constantly exposed. [The British Critic, April 1799]

As a noun, "something isolated," 1890; from earlier adjectival use (1819), which is from Italian isolato or Medieval Latin insulatus.

1800, noun of action from isolate (v.) or else from French isolation, noun of action from isoler (see isolated).