13.3: §89. Adjectives from the Perfect Base (-ORIUS, -IVUS)
1. Just as nouns can have an adjectival suffix in -arius (§38), so can the perfect participle base take a similar adjective-forming suffix in -orius ; in its neuter -orium form, it too can mean “a place for.” The -orius adjective appears as English laudatory, amatory, exclamatory, expository, etc. The noun is seen in auditorium, moratorium (“delay”) , dormitory, laboratory, lavatory, conservatory, observatory, and purgatory (“cleanse”) .
2. The perfect participle could also assume the suffix -ivus , which originally meant “tending to.” Thus from agere , actus came activus (E active , “tending to do”), and from fugere , fugitus came fugitivus (E fugitive , “tending to run away”). The suffix is common in English: motive, captive, decisive, incisive, evocative, deductive, inductive, seductive, putative, interrogative, infinitive, derivative, denominative.