1175-1225;Middle English < Latincircumstantia (circumstant-, stem of circumstāns, present participle of circumstāre to stand round), equivalent to circum-circum- + stā-stand + -nt present participle suffix + -ia noun suffix; see -ance
Word Origin and History for under the circumstances
early 13c., "conditions surrounding and accompanying an event," from L. circumstantia "surrounding condition," neut. pl. of circumstans (gen. circumstantis), prp. of circumstare "stand around," from circum "around" + stare "to stand" from PIE base *sta- "to stand" (see stet). Meaning "a person's surroundings, environment" is from mid-14c. Obsolete sense of "formality about an important event" (late 14c.) lingers in Shakespeare's phrase pomp and circumstance ("Othello" III, iii).
in the circumstances. Given these conditions, such being the case, as in Under the circumstances we can't leave Mary out. This idiom uses circumstance in the sense of “a particular situation,” a usage dating from the late 1300s. It may also be modified in various ways, such as under any circumstances meaning “no matter what the situation,” as in We'll phone her under any circumstances;
under no circumstances, meaning “in no case, never,” as in Under no circumstances may you smoke;
under any other circumstances, meaning “in a different situation,” as in I can't work under any other circumstances; and
under the same circumstances, meaning “given the same situation,” as in Under the same circumstances anyone would have done the same.