Mammoth Uncensored Word List:
24 words ending with r, 17 letters long

abdominoposterior acromioclavicular archaeoastronomer astrophotographer cardioaccelerator chronothermometer echocardiographer microdensitometer microphotographer microspectrometer noncardiovascular nonintramolecular nonmicrofibrillar photolithographer photomicrographer polymorphonuclear scapuloclavicular spectrophotometer spectroradiometer superminicomputer temporomandibular turbosupercharger vestibulocochlear weatherforecaster