How should تَكْرِيرٌ and تَكْرَارٌ be compared?

Six Derived Noun Types: Active/Passive Participles, Comparison, Instrument, Place/Time, and Ṣifah Mushabbahah

• Unrelated roots
• Both passive participles
• Two attested verbal-noun forms from one root
• One imperfect and one active participle