1620s, "a plan or scheme for attaining some end," from contrive + -ance. Meaning "act of contriving" is from 1640s; sense of "the thing contrived, planned, or invented" is from 1660s. Earlier was contrival (c. 1600).
his skillful contrivance of answers to every problem
his testimony was just a contrivance to throw us off the track
the plot contained too many improbable contrivances to be believable