Merriam-Webster Collegiate Dictionary - fortuitous

 adjective  Etymology: Latin fortuitus; akin to Latin fort-, fors chance — more at fortune  Date: 1653  1. occurring by chance  2.  a. fortunate, lucky from a cost standpoint, the company's timing is ~ — Business Week  b. coming or happening by a lucky chance belted down the stairs, and there was a ~ train — Doris Lessing  Synonyms: see accidental  • ~ly adverb  • ~ness noun Usage:  Sense 2a has been influenced in meaning by fortunate. It has been in standard if not elevated use for some 70 years, but is still disdained by some critics. Sense 2b, a blend of 1 and 2a, is virtually unnoticed by the critics. Sense 1 is the only sense commonly used in negative constructions.