Green’s Dictionary of Slang

1. that member of a team of swindlers who poses as an independent individual, ostensibly having no knowledge of their new companions but keenly ready to befriend the victim, often pretending to be drunk.

1591		Greene Notable Discovery of Coosnage in Grosart (1881–3) X 25: So in comes the Barnacle, and taking the cup, drinkes to the Connie, and then faith, what, at cards gentlemen?
1608		Dekker Belman of London F2: He that comes in, and before counterfeited the drunken Barnard is now sober and called the Barnacle.

2. one who speaks through their nose.

1591

Percivall Sp. Dict. n.p.: Gango a barnacle, one that speaketh through the nose [F&H].

3. one who pays too close an attendance, a hanger-on.

1861

M.E. Braddon Trail of the Serpent 4: Slopperton found him a species of barnacle rather difficult to shake off.

4. a decoy swindler, a swindler’s assistant.

1607		Dekker & Webster Northward Hoe III i: Ile cashiere all my young barnicles.
1867		(con. 1600s) M. Lemon Leyton Hall I 233: The man that stood beside thee is old Crookfinger, the most notorious setter, barnacle and foist in the city.

5. (US) one who persists at something.

1896		Arizona Republican (Phoenix, AZ) 9 Jan. 2/2: Barnacles are the cirse of any community.
1904		Mower Co. Transcript (Lansing, MN) 20 Jan. 1/1: Think of the gall of these same barnacles kickin’ because last week the authorities ordered ’em to put in seven hours and a half.
1925		G.H. Mullin Adventures of a Scholar Tramp 131: What a great old train-barnacle he was, that Frisco!
1927		‘Jargon of the Und.’ in DN V 442: Chair barnacle, A bum who sits in railway depot waiting rooms, flophouse halls, and wherever else he may be tolerated.
1930		‘Dean Stiff’ Milk and Honey Route 198: Barnacle — A fellow who sticks to one job a year or more.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 6: Barnacle – a yokel who works one job for a year or more.

6. (US) a former merchant sailor, still ‘stuck to’ his old waterfront haunts .

1945

H.B. Darrach Jr. ‘Sticktown Nocturne’ in Baltimore Sun (MD) 12 Aug. A-1/1: A barnacle is a derelict of the old fleet; it is a point of honor among seamen who have any ‘line’ never to refuse a barnacle a belt.

7. (US Und.) a woman.

1950

Goldin et al. DAUL 132/1: That barnacle (woman) who gave me my bit (prison sentence) on the skin-heist (for rape) was a madam in a nautch-joint (brothel) in Elcart.