Middle English, from Old English andlang "entire, continuous; extended" (adj.); also "alongside of" (prep.); from and- "opposite, against" (from Proto-Germanic *andi-, *anda-, from PIE *anti "against," locative singular of root *ant- "front, forehead") + lang "long" (see long (adj.)).
Reinforced by its Old Norse cognate endlang. The prepositional sense was extended in Old English to "through the whole length of." Of position, "lengthwise," from c. 1200; of movement, "onward," from c. 1300. The meaning "in company, together" is from 1580s. All along "throughout" is attested from 1690s.
1550s, "cannonball" (a sense now obsolete), from French boulette "cannonball, small ball," diminutive of boule "a ball" (13c.), from Latin bulla "round thing, knob" (see bull (n.2)). The meaning "small ball," specifically a metal projectile meant to be discharged from a firearm, is from 1570s. Earliest version of the figurative phrase bite the bullet "do something difficult or unpleasant after delay or hesitation" is from 1891, probably with a sense of giving someone a soft lead bullet to clench in the teeth during a painful operation.
Beggars' bullets—stones thrown by a mob, who then get fired upon, as matter of course. [John Bee, "Slang," 1823]
"going along with, adjoining," by 1782, present-participle adjective from accompany (v.).
"to furnish with a tag," late 14c. (implied in tagged), from tag (n.1). Meaning "go along as a follower" is from 1670s; sense of "follow closely and persistently" is from 1884. Related: Tagging. Verbal phrase tag along is first recorded 1900.