I. adjective
Etymology: past (I) + perfect, adjective
: of, relating to, or constituting a verb tense that is traditionally formed in English with had and denotes an action or state as completed at or before a past time spoken of (as had left in “when he arrived I had left for the city”)
II. noun
1. : the past perfect tense of a language
2. : a verb form in the past perfect tense