moleskin (n.)

type of small burrowing insectivorous mammal (genus Talpa), mid-14c., molle (early 13c. in surnames); perhaps a shortening of obsolete moldwarp, literally "earth-thrower," but this sort of abbreviation is rare at that early age, and perhaps it is rather directly from the root of mold (n.3) "loose earth." It may represent an unrecorded Old English word; compare Middle Dutch mol, molle, Middle Low German mol, mul.

From c. 1600 as a figure of "one who works in darkness" (in Middle English, moldewerpe was figurative of a cleric overly concerned with worldly things). The espionage sense of "secret agent who gradually attains a position deep within organization or nation" was popularized 1974 in John le Carré (but suggested from early 20c.), from the notion of "burrowing."

c. 1200, "animal hide" (usually dressed and tanned), from Old Norse skinn "animal hide, fur," from Proto-Germanic *skinth- (source also of Old English scinn (rare), Old High German scinten, German schinden "to flay, skin;" German dialectal schind "skin of a fruit," Flemish schinde "bark"), from PIE *sken- "to peel off, flay" (source also of Breton scant "scale of a fish," Irish scainim "I tear, I burst"), extended form of root *sek- "to cut."

Ful of fleissche Y was to fele, Now ... Me is lefte But skyn & boon. [hymn, c. 1430]

The usual Anglo-Saxon word is hide (n.1). Meaning "epidermis of a living animal or person" is attested from early 14c.; extended to fruits, vegetables, etc. late 14c. Jazz slang sense of "drum" is from 1927. Meaning "a skinhead" is from 1970. As an adjective, it formerly had a slang sense of "cheating" (1868); sense of "pornographic" is attested from 1968. Skin deep is first attested in this:

All the carnall beauty of my wife, Is but skin-deep. [Sir Thomas Overbury, "A Wife," 1613; the poem was a main motive for his murder]

The skin of one's teeth as the narrowest of margins is attested from 1550s in the Geneva Bible literal translation of the Hebrew text in Job xix.20. To get under (someone's) skin "annoy" is from 1896. Skin-graft is from 1871. Skin merchant "recruiting officer" is from 1792.