"shell-less land snail," 1704, originally "lazy person" (early 15c.); related to sluggard.
"lead bit," 1620s, perhaps a special use of slug (n.1), perhaps on some supposed resemblance. Meaning "token or counterfeit coin" first recorded 1881; meaning "strong drink" first recorded 1756, perhaps from slang fire a slug "take a drink," though it also may be related to Irish slog "swallow." Journalism sense is from 1925, originally a short guideline for copy editors at the head of a story.
"deliver a hard blow with the fist," 1862, from slug (n.3). Related: Slugged; slugging. Slugging-match is from 1878.
To fight with powerful blows; try to smash one another; go toe to toe: The principals were slugging it out in the alley (1943+)
(also slug down): The crowd cheered and jeered and slugged beers (1940s+)
[origin uncertain; perhaps fr the resemblance of a lump of metal to the snail-like creature the slug; the earliest attested US sensesare''goldnugget,lumpofcrudemetal'';thedrink and drinking senses appear to be derived fr phrases like fire a slug and cast a slug, ''take a drink of liquor,'' found as metaphors in late 18th-century British sources, and may be fr Irish slog, ''a drink, a swallow'']
[fr British dialect slog, probably ultimately fr Old English slagan, cognate with German schlagen]