I. adjective
Etymology: past (I) + future perfect, adjective
: of, relating to, or constituting a verb tense that is traditionally formed in English with would have or should have and denotes an action or state completed at a time formerly in prospect (as would have finished in “on Monday I saw that by Friday he would have finished”)
II. noun
1. : the past future perfect tense of a language
2. : a verb form in the past future perfect tense