I'm curious to see how the meanings of some english words have changed over time, but cannot find any sites that list historical definitions. For instance, what was the official definition of the word "civilian" in 1900 versus today? Surely that would have been in an old edition of the Merriam-webster dictionary, so it must be recorded somewhere.
Do any sites exist that let you look back to historical definitions?
The Oxford English Dictionary (OED) includes archaic and obscure definitions of words and includes usages going back as far as possible, as well as notes on etymology. I don't think it will include shifting definitions of technical vocabulary, so legal definitions of "civilian" under international law would probably require specialist literature on that specific question. That being said it does include such definitions as:
3 . Theol. A person who is good or moral as a result of reason or natural inclination rather than the inspiration of Christian belief. Cf. civil adj. 16. Obs.
a. More fully Indian civilian. Originally: a member of the civil service of the East India Company. Later: a member of the Indian Civil Service. Now hist.
A practitioner of Roman civil law, or of any of the various legal systems or codes historically derived from Roman civil law; an expert in or student of this. See civil law n. 1.
as well as the now more common: