Green’s Dictionary of Slang

1. a lock of hair which is carefully curled then covered with soap to make it lie flat; in pl., such a hairstyle, as favoured by the New York gangs of the period.

1840		N.O. Picayune 30 Aug. 2/2: Howard [...] is described as [...] wearing moustaches and soaplocks [DA].
[1846		Swell’s Night Guide 64: A spicy tile, and nobby head of hair. / Side curls all slap, faked up with fogo’d soap].
1848		Bartlett Dict. Americanisms 319: soap-lock. A lock of hair made to lie smooth by soaping it.
1861		Oregon Argus 10 Aug. n.p.: So as to give their disheveled soap locks a peculiarly forky and warlike appearance.
1872		Schele De Vere Americanisms 323: The rowdy of America differs little from his brother in the Old Country, except, perhaps, in the one point of wearing frequently a soaplock, a lock of hair which he makes to lie smoothly by means of soap.
1876		Manchester Courier 20 Sept. 3/3: Two hay-coloured dabs of hair, one on each temple, known to scientific explorers of the New York Bowery as ‘soap-locks’.
1891		S.M. Welch Recollections of Buffalo 1830-40 30: [Dickens wore] long hair and earlocks which were then denominated as ‘soap-locks,’ but deemed vulgar, except for the dudes and ‘Bowery boys’ of those days.

2. attrib. use of sense 1.

1841		N.Y. Herald 16 Nov. 2/5: The soaplock fashion of wearing the hair is about coming again into practice among the ‘round rimmers.’.
1871		H. Strange Irene 47/1: All those soaplock college boys and fortune-hunters who are for ever dangling around her?

3. someone who wears this hairstyle, thus a gang member, a thug.

1839		Morn. Herald (NY) 26 Nov. 2/2: White [...] was one of that infamous class of characters [...] ‘soap locks,’ ‘round rimmers,’ ‘fire rowdies,’ etc.
1840		Congressional Globe 2 Apr. Appendix 376: In that living, moving, ranting band, the boys, negroes, loafers, and a new species of the same animal, familiarly known in the city of New York as soap-locks, took the lead.
1840		N.Y. Daily Express 13 Aug. 2/6: John A. Patterson, one of the order of ‘soaplocks,’ [is arrested].
1841		in Life in the West (1842) 120: Zay, command that soaplock at the bar to [...] present me with my gin sling immediately.
1848		Bartlett Dict. Americanisms 319: soap-lock. [...] A name given to a low set of fellows who lounge about the markets, engine-houses, and wharves of New York, and are always ready to engage in midnight rows or broils. It is, in fact, but another name for a Rowdy or Loafer. The name comes from their wearing long side locks, which they are said to smear with soap, in order to give them a sleek appearance; whence the name.
1852		Knickerbocker (NY) xl (Aug.) 187: There is something very ‘Bowery-boy’-ish in a question asked by one ‘soap-lock’ of another.
1888		Troy Daily Times 3 Feb. n.p.: When I first came to this city, the dangerous class was the soap-lock [JSF].
1948		(ref. to 1844) Sat. Rev. Lit. (US) 17 July 23: An 1844 watercolor of Broadway idlers, ‘The Soap Locks’ [DA].

4. attrib. use of sense 3.

1842		Whip and Satirist of N.Y. & Brooklyn 19 Mar. 3/1: The satisfaction, we are told, was tendered by Prince John Davis, in the name and on the behalf of one of young Mott’s soap-lock companions, and the arrangement was assented to by Justice Stevens.
1846		D. Corcoran Pickings from N.O. Picayune 165: William Weithman, a loafer of the upper crust soap-lock order.
1850		J. Weir Lonz Powers I 31: I would give my first $100 fee to be in at the dissection of a ‘broken soaplock heart.’.