Mammoth Uncensored Word List:
23 words ending with a, 17 letters long

antischizophrenia choriocarcinomata counterpropaganda craniopharyngioma hemiachromatopsia hyperglobulinemia hyperphosphatemia hypochondroplasia lymphangiosarcoma lymphoepithelioma lymphogranulomata macroglobulinemia medulloblastomata methemoglobinemia nonproteobacteria oligodendroglioma phaeochromocytoma pseudohydrophobia siderodromophobia teratocarcinomata trichopathophobia trimethylaminuria triskaidekaphobia