1.AdjectiveOccurring around the middle of the century. (Elliptically refers to whichever century is evident from the context of a discussion.)
"midcentury modern; This midcentury masterpiece was overlooked at the time it was created.; This ashtray is very midcentury, but that lamp is the most midcentury thing I've seen all year."
2.NounThe midpoint or middle portion of a century.
"at midcentury; She wrote an essay taking stock of the movement at midcentury."