Fortuitous

прилагательное [литературно-книжное] случайный, неожиданный Синоним(ы): accidental, casual

Большой англо-русский словарь

Fortuitous

adjective Etymology: Latin fortuitus; akin to Latin fort-, fors chance — more at fortune 1. occurring by chance 2. a. fortunate, lucky Example: from a cost standpoint, the company's timing is fortuitous — Business Week b. coming or happening by a lucky chance Example: belted down the stairs, and there was a fortuitous train — Doris Lessing Synonyms: see accidentalfortuitously adverbfortuitousness 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.

Merriam-Webster's Collegiate Dictionary