This is the 2552nd most frequent Spanish word.
casualidad
Chance or coincidence.
Here, 'casualidad' is used to express an unexpected and unplanned occurrence.
Fue una simple casualidad que nos encontráramos en la misma cafetería.
It was a mere coincidence that we met at the same café.
In this sentence, 'casualidad' refers to something happening without intention or planning.
Por casualidad, encontré un libro que había estado buscando por años.
By chance, I found a book I had been searching for for years.
Here, 'casualidad' conveys the possibility of encountering someone or something unexpectedly.