Fortuitous: This word means “occurring by chance,” but its resemblance
to fortune has given it an adopted sense of “lucky.”
For meticulous adherence to the traditional meaning, use fortuitous only
in the sense indicated in this sentence: “His arrival at that moment was
fortuitous, because her note had not specified the exact time of her departure.”
Nothing in the context qualifies his arrival as fortunate; the sentence merely
states that he arrived in time without knowing that he would do so.
The informal meaning is expressed here: “His fortuitous arrival
at that very moment enabled him to intercept the incriminating letter.” In this
sentence, the time of his appearance is identified as a lucky stroke.
