/ ˈspuːnərɪzəm; NAmE / noun
a mistake in which you change around the first sounds of two words by mistake when saying them, often with a humorous result, for example well-boiled icicle for well-oiled bicycle
ORIGIN: Named after W.A. Spooner (1844–1930), the head of New College, Oxford, who was said to make many mistakes like this when he spoke.