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elephant [elephant 词源字典]: elephant: [13] Elephants were named from their tusks. Greek eléphās (probably a borrowing from a non-Indo-European language) meant originally ‘ivory’ (hence chryselephantine ‘of gold and ivory’ [19]). Only later did it come to denote the animal itself, and it passed in this sense into Latin as elephantus. By post-classical times this had become *olifantus, and it is a measure of the unfamiliarity of the beast in northern Europe in the first millenium AD that when Old English acquired the word, as olfend, it was used for the ‘camel’.

Old French also had olifant (referring to the ‘elephant’ this time) and passed it on to English as olifaunt. It was not until the 14th century that, under the influence of the classical Latin form, this began to change to elephant. In the 16th and 17th centuries there was a learned revival of the sense ‘ivory’: Alexander Pope, for instance, in his translation of the Odyssey 1725, refers to ‘the handle … with steel and polish’d elephant adorn’d’.

The notion of the white elephant as ‘something unwanted’ arose apparently from the practice of the kings of Siam presenting courtiers who had incurred their displeasure with real white elephants, the cost of whose proper upkeep was ruinously high.
[elephant etymology, elephant origin, 英语词源]
ruinous (adj.): late 14c., "going to ruin," from Old French ruinos (Modern French ruineux) or directly from Latin ruinosus "tumbling down, going to ruin," from ruina (see ruin (n.)). Meaning "causing ruin" is from mid-15c. Related: Ruinously.
white elephant (n.): "burdensome charge, inconvenient thing that one does not know how to get rid of," 1851, supposedly from the practice of the King of Siam of presenting one of the sacred albino elephants to a courtier who had fallen from favor; the gift was a great honor, but the proper upkeep of one was ruinously expensive.