Sewage, Sewerage
These words have distinct meanings. Sewage refers to the contents of the sewer; sewerage to the system of sewers.
Sociable, Social
“He is one of the most sociable men I have met. He is fond of society, and is very ready in conversation.” Sociable means companionable; social applies to the relations of men in society; as social duties, social pleasures, social interests.
Specialty, Speciality
These words are interchangeable, but the former is the better word.
Requirement, Requisition, Requisite
While these words have something in common, each has a meaning peculiar to itself. Requirement means that which is required as an essential condition, or as something necessary; requisition, that which is required as of right, a demand or application made as by authority; requisite, that which is required by the nature of things, or by circumstances, that which cannot be dispensed with. “She understood the nature of the child and of its requirements.” “The officer made a requisition for more troops.” “This is as much a requisite as food and clothing.”
Sick, Ill
There is a growing tendency to discriminate between sickness and illness, limiting the words sick and sickness to some slight disturbance of the physical system, as nausea, and applying the words ill and illness to protracted disease and disordered health.