Where does the idiom "smacks of x" come from?

Solution 1:

It is an old figurative usage of smack (late 16th century) meaning to "smell", to "taste". The common idea that it may derive from smacking the lips before tasting something is wrong according to the following source:

Smack:

• mid-13c., "to smell (something"); mid-14c., "to taste (something), perceive by taste" (transitive); late 14c. "to have a taste, taste of" (intransitive), ......... Old High German smakken "have a savor, scent, or taste," German schmecken "taste, try, smell, perceive." Sometimes also smatch.

• Now mainly in verbal figurative use smacks of ... (first attested 1590s). "Commonly but erroneously regarded as identical with [smack (n.2)], as if 'taste' proceeds from 'smacking the lips.'" [Century Dictionary]

(Etymonline)

The following quote is from Shakespeare's Henry IV, Part 2, Scene 1 (1600):

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