The vicissitudes of Irish lexicography are not without amusing incident, for the glosses are often the helpless guesses of men as ignorant as we are of the meaning of words that had dropt out of usage with the decay of the customs to which they had reference. One of the most fatal methods of procedure current in these glosses is the assignment of an important role to the assumed derivation of the word, the glossator often bringing no mental effort to bear on the facts, but emmiting his speculations in the most indifferent or audacious spirit. Of course, not all faults lie at the door of the Irish original scribe; the later copyist has many sins to answer for.
-- Robert Atkinson, 1885: Irish Lexicography: an Introductory Lecture