1564, "opponent of Anglican hierarchy," later applied opprobriously to "person in Church of England who seeks further reformation" (1571), probably from
purity (q.v.). After c.1592, applied to anyone deemed overly strict in matters of religion and morals.
"The Puritan hated bear-baiting, not because it gave pain to the bear, but because it gave pleasure to the spectators." [Thomas Babington Macaulay, "History of England," 1849]
Puritanism (1573) was famously defined by H.L. Mencken as "the haunting fear that someone, somewhere may be happy" (1920).