a viscous liquid, 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), probably a derivation of *trewo-, from PIE *derw-, variant of root *deru- "be firm, solid, steadfast," with specialized senses "wood, tree" and derivatives referring to objects made of wood.
Tar baby "a sticky problem," also a derogatory term for "black person," is from an 1881 "Uncle Remus" story by Joel Chandler Harris. Tarheel for "North Carolina resident" first recorded 1864, probably from the gummy resin of pine woods. Tar water, an infusion of tar in cold water, was popular as a remedy from c. 1740 through late 18c.
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.