WordNet sense 1 (around the middle of a scale of evaluation of physical measures):

average, medium

WordNet sense 2 (being within reasonable or average limits; not excessive or extreme):

moderate, moderate

WordNet sense 3 (being neither at the beginning nor at the end in a series):

mediate, middle

WordNet sense 4 (act between parties with a view to reconciling differences):

arbitrate, intercede, liaise