Definitions
American Heritage® Dictionary of the English Language, Fourth Edition
- n. A very large whalebone whale (Balaenoptera musculus) having a bluish-gray back, yellow underparts, and several ventral throat grooves. It is considered the largest living animal, sometimes reaching a length of 30.5 meters (100 feet). Also called sulphur-bottom.
Wiktionary
WordNet 3.0
- n. largest mammal ever known; bluish-grey migratory whalebone whale mostly of southern hemisphere
Examples
“An unexpected beat on a snare drum made a French horn splutter out a belching sound, and in the back of the band something big emitted a snort, one that made Lisa think of a blue whale that had just surfaced after a week underwater.”
Lists
These user-created lists contain the word ‘blue whale’.
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tHe Best Animals Ever
giraffe, elepant, cattle, water buffalo, langur monkey, baboon, lion, antelope, cheetah, tapeworm, kangaroo, bullfrog and 95 more...
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Endangered Species
bilby, snow leopard, Salt Creek tiger ..., Siberian tiger, blue whale, giant panda, African wild dog, crowned solitary ..., chained_bear, albatross, black-footed ferret
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It's a small...
shetland pony, cornish hen, miniature schnauzer, toy poodle, african pygmy goat, world after all, pocket pig, blue whale, cama

Prolagus Oh, well, I don't know which kind of blue whales you usually meet... Apr 23, 2008
asativum Come to think of it, blue whales do look a little mousy.
Mussels, not so much. Apr 19, 2008
Prolagus It's interesting to note that the blue whale and the house mouse share the specific name musculus (binomial names are respectively Balænoptera musculus and Mus musculus). Both names were chosen by Linnæus (Carl von Linné) in the XVIII century.
The word is a diminutive of Latin mus (mouse), so there is no need for explanation for using it for the house mouse. But what about blue whales?
The explanation relies on the fact that, in Latin, musculus also means muscle; and this is the meaning it has in the blue whale's scientific name.
Apparently, in the past, ...the shape and movement of some muscles (notably biceps) were thought to resemble mice... (From: Online Etymology Dictionary).
What is also interesting is that the same double meaning/common root is present in other languages: Greek, Armenian, German, Arabic. Apr 17, 2008