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20 words ending with ss, 18 letters long

comprehensibleness expressionlessness extemporaneousness forethoughtfulness hyperconsciousness hypersensitiveness inappreciativeness inconsiderableness indestructibleness indiscriminateness interconnectedness irreconcilableness irreproachableness nondestructiveness overprotectiveness representativeness uncompromisingness unconscionableness unintelligibleness unsatisfactoriness