Crabs and their close relatives have 10 legs, arranged in five pairs. Some of their legs are used for walking, while others are used for swimming or defense.
Definition of plunge for English Language Learners. : 1  a sudden fall or jump usually from a high place. : 2  a sudden quick fall in amount, value, etc. : 3  the act of suddenly beginning to be in a particular condition or situation.
Word Origin & History plunge c.1380, from O.Fr. plungier (c.1140), from V.L. *plumbicare to heave the lead, from L. plumbum lead (see plumb). Original notion perhaps is of a sounding lead or a fishing net weighted with lead. Fig. use in take the plunge commit oneself is from 1845. Plunger as a mechanism is from 1777. Plunging neckline attested from 1949.