Meaning

adverb and nothing more

adjective being the only one; single and isolated from others

adverb without any others being included or involved

originFrom Middle English oonly, only, from Old English ānlīċ, ǣnlīċ (“only; singular; solitary”), from Proto-Germanic *ainalīkaz. Cognate with obsolete Dutch eenlijk, German ähnlich (“similar”), Old Norse álíkr, Swedish enlig (“unified”). By surface analysis, on(e) + -ly. * Regarding the different phonological development of only and one, see the note in one.

Etymology from Wiktionary, CC BY-SA 3.0