WordNet sense 1 (a statistic describing the location of a distribution):

norm

WordNet sense 2 (amount to or come to an average, without loss or gain):

average out

WordNet sense 3 (lacking exceptional quality or ability):

fair, mediocre, middling

WordNet sense 4 (not exceptional in any way especially in quality or ability or size or degree):

ordinary

WordNet sense 5 (relating to or constituting the most frequent value in a distribution):

modal

WordNet sense 6 (relating to or constituting the middle value of an ordered set of values (or the average of the middle two in a set with an even number of values)):

median

WordNet sense 7 (approximating the statistical norm or average or expected value):

mean

WordNet sense 8 (conforming with or constituting a norm or standard or level or type or social norm; not abnormal):

normal

WordNet sense 9 (around the middle of a scale of evaluation of physical measures):

intermediate, medium, intermediate

WordNet sense 10 (being within reasonable or average limits; not excessive or extreme):

moderate, moderate

WordNet sense 11 (having no special distinction or quality; widely known or commonly encountered; average or ordinary or usual):

common