A naval or nautical dish, possibly a type of food made from broken biscuits and salt meat; or a foolish person (naval slang).
A nautical term, possibly combining 'dunder' with 'funk' (from Dutch 'fonk' meaning spark, or referring to a state of panic). The word may derive from old sailor's vocabulary describing both food and foolish behavior.
Old ships had their own vocabulary for weird food and weird people—'dunderfunk' is one of those marvelous nautical words that scholars argue about, possibly describing both a desperate sailor's meal and a desperately foolish sailor.
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