Synonyms for Middling (same or very similar meaning)
WordNet sense 1 (lacking exceptional quality or ability):
average, fair, mediocre
WordNet sense 2 (not exceptional in any way especially in quality or ability or size or degree):
ordinary
WordNet sense 3 (to a moderately sufficient extent or degree):
fairly, moderately, passably, reasonably, somewhat, within reason
From the ODE community, based on WordNet
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