casual
adjective
1 (fortuito) chance
un encuentro casual a chance encounter; es un hecho casual y aislado it's an isolated, chance happening; su éxito no es casual, sino fruto del trabajo his success cannot be put down to chance but is the product of hard work; el descubrimiento de la obra fue casual the work was discovered by chance; nada es casual nothing happens by chance; de forma o manera casual by chance
no es casual que ... it's no coincidence that ...
por un casual by any chance