The ARY / ORY Rule (Major)

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

The ARY / ORY Rule

English Spanish Helpful Reminders
...ary ...ario
...ory ...orio
Accusatory Acusatorio only 1 C
Adversary Adversario
Ambulatory Ambulatorio also Ambulante
Anniversary Aniversario only 1 N
Appelatory Apelatorio only 1 P
Benedictory Benedictorio
Canary Canario
Category Categoría feminine gender *
Castigatory Castigatorio
Centenary Centenario
Compensatory Compensatorio
Conciliatory Conciliatorio
Confiscatory Confiscatorio
Conservatory Conservatorio
Contrary Contrario
Crematory Crematorio
Culinary Culinario
Declamatory Declamatorio
Defamatory Difamatorio I for E
Derogatory Derogatorio
Directory Directorio
Dormitory Dormitorio
Elementary Elementario also Elemental
Eliminatory Eliminatoria
Emasculatory Emasculatorio
Factory Factoría See note **
Fulminatory Fulminatorio
Gesticulatory Gesticulatorio
Glory Gloria feminine gender *
History Historia feminine gender *
Illusory Ilusorio only 1 L
Inflammatory Inflamatorio only 1 M
Laboratory Laboratorio
Mammary Mamario only 1 M
Mandatory Mandatorio
Maxillary Maxilario only 1 L
Moratory Moratorio ***
Obligatory Obligatorio
Observatory Observatorio
Octogenary Octogenario
Olfactory Olfactorio
Offertory Ofertorio only 1 F
Ordinary Ordinario
Parliamentary Parlamentario different spelling
Plagiary Plagiario
Penitenciary Penitenciaría feminine gender
Postulatory Postulatorio
Proprietary Propietario different spelling
Pulmonary Pulmonario
Pulsatory Pulsatorio
Purgatory Purgatorio
Questionary Cuestionario C for Q
Refectory Refectorio
Refractory Refractario different spelling
Regulatory Regulatorio
Respiratory Respiratorio
Salutatory Salutatorio
Secretary Secretario
Sensory Sensorio
Solitary Solitario
Speculatory Especulatorio quirk #6
Subsidiary Subsidiario
Summary Sumario only 1 M
Supervisory Supervisorio
Temporary Temporario also Temporal
Terminatory Terminatorio

Although there are perhaps less than three hundred words in English with these endings, this Rule is extremely accurate. There are very few exceptions. These are some relevant ones:

English Spanish Helpful Reminders
Armory Armería
Gory Aparatoso
Predatory Depredador
Retaliatory Vengativo
Story Cuento
Savory Sabroso
Doesn't it feel wonderful to be writing in a "foreign" language?!

*You may have noticed that more of those femenine gender words creeped in - we must to clear that up! Chapter Eighteen night help, if you are in a hurry. Otherwise, just read on with the rest of us!
** The word "factory" is translated above to Spanish as "factoría". This word, although correct, is rarely used. The modern usage would be "fábrica", a place where things are fabricated! (We've learned that FABRICATE translates to FABRICAR [Chapter Three]. In Englisll of course, Fabricate means to manufacture, or make, something.
***Moratorium is also Moratorio in Spanish.