I encountered this world a while back on Quora, but really cannot remember what is was, which is terribly bugging me. It is used to mean something that has been present or practiced since a certain period in the past, and is perhaps now anachronistic.
To reiterate, it was a phrasal noun (that is, something like "carry-over" or "leftover").
Edit to clarify the meaning of the term "phrasal noun":
It is a noun made up of a verb and a preposition either preceding or succeeding the former. If the preposition precedes the verb (as in "onset", for example), there is no hyphen between the two. If the preposition succeeds it, there may or may not be a hyphen).
It isn't "artefact" or "hand-me-down". It's not a physical object that the word refers to, it's a practice, custom or law, and, as mentioned above, it conveys the idea of the outdatedness.