Longman Dictionary of Contemporary English
WordNet
n. a great European painter prior to 19th century
Wikipedia
In theory an Old Master should be an artist who was fully trained, was a Master of his local artists' guild, and worked independently, but in practice paintings considered to be produced by pupils or workshops will be included in the scope of the term. Therefore, beyond a certain level of competence, date rather than quality is the criterion for using the term.
Usage examples of "old master".
Still, when the old Master saw how patient Robinton was with some of the more backward students, he began to mellow a trifle.
A crowd of angry students behind the old Master raised voices like a cacophony of crows at the sight of him.
What she said Raederle did not hear, only the silence that was passed like a tangible tiling from Master to Master, from group to group in the room until there was not a sound in the room except one very old Master&rsquo.
Yet I could scarce choose but laugh, when my old master passed so near to me, dreaming all the while that Gurth was keeping his porkers many a mile off, in the thickets and swamps of Rotherwood.
Come, my old master, let us take a glass, and after that we will continue our philosophical disquisitions.