unlike orthography and orthoepy [why does orthoepy have two(2) accepted pronunciations?!], most etymologies are consistent between major dictionaries (OED, W3, AHD, etc.) -- the OED, with its unlimited space, just has a bit more of the same. so, fwiw:

sardine - [a. F. sardine, ad. It. sardina:L. sardna (Columella; cf. late Gr. ? and
? ), f. sarda, = Gr.?, the sardine or some similar fish. In the 17th and
18th c. the Italian form was often used.
The Latin and Greek word may be related to the name of the island, L. Sardinia, Gr.?:
cf. SARD a.]

sardonic - [a. F. sardonique (16th c.) = Sp. sardónico, Pg., It. sardonico, as if ad. L.
*sardonicus, an alteration (by substitution of suffix: see -IC) of sardonius: see
SARDONIAN.
Hobbes's form sardanique is assimilated to Gr. ?: see prec.]
{sardonian} [f. L. sardoni-us + -AN.
The Latin adj. is ad. Gr. ? Sardinian, which in late Gr. was substituted for ?
(Homer, etc.; of obscure origin), as the descriptive epithet of bitter or scornful laughter; the motive
of the substitution was the notion that the word had primary reference to the effects of eating a
‘Sardinian plant’ (L. herba Sardonia or Sarda), which was said to produce facial convulsions
resembling horrible laughter, usually followed by death.]


btw, OED acknowledges that sardonic has a transferred sense: Hence of a person, personal
attribute, etc.: Characterized by or exhibiting bitterness, scorn or mockery.

-joe saturnine

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