imperfect vs unretentive

imperfect

adj
  • not perfect 

  • belonging to a tense of verbs used in describing a past action that is incomplete or continuous 

  • known or expected to be polyphyletic, as of a form taxon. 

  • unisexual: having either male (with stamens) or female (with pistil) flowers, but not with both. 

noun
  • something having a minor flaw 

  • a tense of verbs used in describing a past action that is incomplete or continuous 

verb
  • to make imperfect 

unretentive

adj
  • Not retentive 

How often have the words imperfect and unretentive occurred in a corpus of books? (source: Google Ngram Viewer )