Etymologists say the letter "P" gradually replaced the word "C" in "cod," but they aren't sure why. Anatoly Liberman, author of "Word Origins and How We Know Them" (Oxford University Press, 312 pages, $25), says people may have favored the "P" in "pod" because it matched the sound of "pea," which is often paired with "pod." More subtly, Liberman says, "pod" might have emerged because it sounded similar to words such as "pad," "pudge," "pot" and "pudding." "Numerous English words referring to swollen objects, protrusion, and the like have the structure P + Vowel + Consonant," Liberman writes by e-mail. This sound structure, he says, may have "suggested fatness to the speakers of Germanic [languages]."