tar (n.1)

type of thick, viscous, dark-colored liquid used as a salve (for sheep), caulking agent (for ships), and incendiary material, Middle English tēr, from Old English teoru, teru "tar, bitumen, resin, gum," literally "the pitch of (certain kinds of) trees," from Proto-Germanic *terw- (source also of Old Norse tjara, Old Frisian tera, Middle Dutch tar, Dutch teer, German Teer).

According to Watkins this is probably a derivation of *trewo-, from PIE *derw-, a variant of the root *deru- "be firm, solid, steadfast," with specialized senses "wood, tree" and derivatives referring to objects made of wood.

Tar baby "a sticky problem" (American English) was popularized by a Joel Chandler Harris "Uncle Remus" story (1881), but the story and the idea are older in Black folklore (the dialect story was printed earlier as part of "Bushy and Jack" in Harper's Monthly Magazine, May, 1867, attributed to Mary Hose). It is attested by 1948 as a derogatory term for "Black person."

To beat (or knock) the tar out of someone is attested by 1884; the tar is perhaps euphemistic.

also Jack Tar, "sailor," 1670s, probably a special use of tar (n.1), which stuff was a staple for waterproofing aboard old ships (knights of the tarbrush being a jocular phrase for "sailors"); or possibly a shortened form of tarpaulin, which was recorded as a nickname for a sailor in 1640s, from the tarpaulin garments they wore.

Middle English terren, from late Old English tirwan, "to smear with tar," from tar (n.1).

To tar and feather (1769) was famously a mob action in America in Revolutionary times (used by both sides) and for several decades thereafter. The punishment is prescribed in an ordinance of Richard I (1189), but the exact verbal phrase is not attested until 18c. Related: Tarred; tarring.