from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An archaic progressive construction in middle voice (syntactically active but semantically passive), replaced by the passive progressive in modern English. For example, "the house is building", "the meal was eating", "the trunks were carrying down" (today "the house is being built", "the meal is being eaten").
from The Century Dictionary and Cyclopedia
- In grammar, of or pertaining to the passive voice.
passive + -al (Wiktionary)