This Rule applies to those words in English with two or more syllables that end in
....ary
or
....ory
To translate them into Spanish, we will substitute the ending ...ary with
...ario
Thus, the English word ordinary is the Spanish word ordinario.
and we will substitute the ending ...ory with
...orio
and the English word accesory is the Spanish word accesorio.
Some further (mixed) Examples