【Medium】 ,  【middling】 ,  【mediocre】 ,  【second-rate】 ,  【moderate】 ,  【average】 ,  【fair】 ,  【indifferent】  mean midway, or about midway, between the extremes of a scale or measurement or evaluation.

【Medium】 usually presupposes reference to some scale of measurement or comparison, whether by literal use of an instrument, or through mental power of measuring or gauging attained by experience.

【Middling】 is seldom used when accurate measurement or gradation is implied; it is employed chiefly in estimations (as of quality, rank, or value) to describe what is as far removed from the worst or lowest as it is from the best or highest. It may appropriately describe something that fails to measure up to the best or the first rate yet does not merit disapproval or rejection.

In commercial use 【middling】 sometimes specifically designates the second of three grades.

【Mediocre】  tends to be more depreciative than  【middling】 ; thus, one who describes a moving picture as  【middling】  implies that it was good, but far from excellent, but one who describes it as  【mediocre】 gives ground for the inference that it was distinctly less than what one might call good. Often the word is modified by an adverb of degree.

【Second-rate】 implies a ranking midway between extremes regarded as first-rate and as third-rate.

Frequently  【second-rate】  loses all suggestion of a position on a scale of rating and then connotes inferiority and is used interchangeably with  【mediocre】 .

【Moderate】  (see also  【MODERATE】 1 ) stresses limitations in quality, intensity, or degree; it implies distance from the extreme or from either of the extremes possible to a thing of its kind.

【Average】  (see also under  【AVERAGE】  ) implies a theoretical level at which all things of a given kind, class, or category would find themselves or would seek, if their inequalities were resolved.

However the term is applied more often to what seems of the common run or is undistinguished either by its superiority or its inferiority, or is not exceptional or outstanding in any way; thus, a man of  【average】 ability seems to have neither greater nor less ability than that of the ordinary man.

【Fair】 is applied to what is neither notably good nor bad, excellent nor poor, large nor small; often, only the context can reveal whether the implication is one of adequacy or of deficiency.

【Indifferent】 is applied to what is difficult to rate because it is completely unimpressive, warranting neither praise nor censure.