The sardonic sardine
Something I just learned: "sardonic" and "sardine" are etymologically related. "Sardine," unsurprisingly, appears to be related to the island of Sardinia, near which sardines were often fished. (The Oxford English Dictionary cautiously says they "may" be related, but the American Heritage is more confident.)
And "sardonic" also relates to Sardinia, because of a Sardinian plant (in Latin, the OED tells us, "herba Sardonia or Sardōa"), which supposedly "produce[d] facial convulsions resembling horrible laughter, usually followed by death." Quite the island.
Of course, "candidate" is also etymologically related to the organism that causes yeast infections.