Apology, n.: (1533-1594)

        The OED tracks a cultural shift in the meaning of the noun, "apology," from "a defense or vindication" to "an explanation expressing regret for offense"  As with many loan words (this one from the Greek apologia), the borrowing language is free to shift its meaning to cover newly arising cultural needs.  Since the verbs "to defend" and "to vindicate" already had been successfully borrowed from Latin to speak for their EModE and ModE needs, the more obscure apologia began to be used more often to describe a speech uttered for actions which were, by implication, ultimately indefensible and regretted.  Why?  The reason might have to do with the re-socialization of the actions of offense and regret as the noble culture of the duel, and the commoner culture of fisticuffs and feud, became increasingly unacceptable in Modern culture.  A third path had to be found and named to thread the passage between a successful defense which countered the accusation of offense and the violent retribution which, according to noble codes of "honor" and commoner codes of "justice," must follow a successful demonstration that an offense occurred.  The result was the modern "apology."  Sidney was not "apologizing for poetry" in the modern sense, and someone apparently sensed the word's shifting implication of such an apology in the first title.