emeraldyoudaoicibaDictYouDict[emerald 词源字典]
emerald: [13] Emerald traces its history back to an ancient Semitic verb ‘shine’ – bāraq. From this there seems to have been formed a noun *bāraqt meaning ‘gem’. This was taken over into the ancient vernacular languages of India (main source of gems in early times) as maragada-. Greek acquired the word as máragdos ‘green gem’, which was soon superseded as the main form by a variant smáragdos.

Latin adopted this as smaragdus (which passed into English, probably via Old French, as smaragd, a term used for the ‘emerald’ from the 13th to the 18th century, and revived as an archaism in the 19th century). In post-classical times Latin smaragdus became *smaralda, and as this became disseminated through the Romance languages it acquired in many cases an additional syllable: Spanish esmeralda, for instance (source of the English forename) and Old French esmeraude, borrowed into Middle English as emeraud.
[emerald etymology, emerald origin, 英语词源]
emerald (n.)youdaoicibaDictYouDict
"bright green precious stone," c. 1300, emeraude, from Old French esmeraude (12c.), from Medieval Latin esmaraldus, from Latin smaragdus, from Greek smaragdos "green gem" (emerald or malachite), from Semitic baraq "shine" (compare Hebrew bareqeth "emerald," Arabic barq "lightning").

Sanskrit maragdam "emerald" is from the same source, as is Persian zumurrud, whence Turkish zümrüd, source of Russian izumrud "emerald." For the excrescent e-, see e-.
In early examples the word, like most other names of precious stones, is of vague meaning; the mediæval references to the stone are often based upon the descriptions given by classical writers of the smaragdus, the identity of which with our emerald is doubtful. [OED]
Emerald Isle for "Ireland" is from 1795.