Of medium size, not particularly large or small(adjective)
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Use "midsized" in a sentence
"Despite a handful of new listings, technology investors with stakes in midsized growth companies are wondering if the warm IPO market of past years will ever return, even if it never approaches the heights of the wild late-1990s boom era again."
"This annual migration is bigger than the hajj, its financial impact enough to make or break a midsized country."
"The virtualization platform providers are going to have to adapt their go-to-market strategies to this ever-changing dynamic, as new growth opportunities open up around new deployment of virtualized servers not specifically targeted at consolidation, and at new customer segments such as midsized companies."