The Collaborative International Dictionary of English v.0.48:

Chap \Chap\ (ch[o^]p), n. [OE. chaft; of Scand. origin; cf. Icel
   kjaptr jaw, Sw. K[aum]ft, D. ki[ae]ft; akin to G. kiefer, and
   E. jowl. Cf. Chops.]
   1. One of the jaws or the fleshy covering of a jaw; --
      commonly in the plural, and used of animals, and
      colloquially of human beings.
      [1913 Webster]

            His chaps were all besmeared with crimson blood.
                                                  --Cowley.
      [1913 Webster]

            He unseamed him [Macdonald] from the nave to the
            chaps.                                --Shak.
      [1913 Webster]

   2. One of the jaws or cheeks of a vise, etc.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chap \Chap\ (ch[a^]p or ch[o^]p), v. t. [imp. & p. p. Chapped
   (ch[a^]pt or ch[o^]pt); p. pr. & vb. n. Chapping.] [See
   Chop to cut.]
   1. To cause to open in slits or chinks; to split; to cause
      the skin of to crack or become rough.
      [1913 Webster]

            Then would unbalanced heat licentious reign,
            Crack the dry hill, and chap the russet plain.
                                                  --Blackmore.
      [1913 Webster]

            Nor winter's blast chap her fair face. --Lyly.
      [1913 Webster]

   2. To strike; to beat. [Scot.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chap \Chap\, v. i.
   1. To crack or open in slits; as, the earth chaps; the hands
      chap.
      [1913 Webster]

   2. To strike; to knock; to rap. [Scot.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chap \Chap\, n. [From Chap, v. t. & i.]
   1. A cleft, crack, or chink, as in the surface of the earth,
      or in the skin.
      [1913 Webster]

   2. A division; a breach, as in a party. [Obs.]
      [1913 Webster]

            Many clefts and chaps in our council board. --T.
                                                  Fuller.
      [1913 Webster]

   3. A blow; a rap. [Scot.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chap \Chap\ (ch[a^]p), n. [Perh. abbreviated fr. chapman, but
   used in a more general sense; or cf. Dan. ki[ae]ft jaw,
   person, E. chap jaw.]
   1. A buyer; a chapman. [Obs.]
      [1913 Webster]

            If you want to sell, here is your chap. --Steele.
      [1913 Webster]

   2. A man or boy; a youth; a fellow. [Colloq.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chap \Chap\, v. i. [See Cheapen.]
   To bargain; to buy. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

chap
    n 1: a boy or man; "that chap is your host"; "there's a fellow
         at the door"; "he's a likable cuss"; "he's a good bloke"
         [syn: chap, fellow, feller, fella, lad, gent,
         blighter, cuss, bloke]
    2: a long narrow depression in a surface [syn: crevice,
       cranny, crack, fissure, chap]
    3: a crack in a lip caused usually by cold
    4: (usually in the plural) leather leggings without a seat;
       joined by a belt; often have flared outer flaps; worn over
       trousers by cowboys to protect their legs
    v 1: crack due to dehydration; "My lips chap in this dry
         weather"

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "chap":
   Adamite, abysm, abyss, arroyo, bastard, being, bird, bloke, body,
   box canyon, boy, bozo, breach, break, buck, buddy, bugger, canyon,
   cat, cavity, character, chasm, check, chimney, chink, cleft,
   cleuch, clough, col, coulee, couloir, cove, crack, cranny,
   creature, crevasse, crevice, customer, cut, cwm, defile, dell,
   dike, ditch, donga, draw, duck, earthling, excavation, fault,
   feller, fellow, fissure, flaw, flume, fracture, furrow, gap, gape,
   gash, gazebo, gee, geezer, gent, gentleman, gorge, groove,
   groundling, gulch, gulf, gully, guy, hand, he, head, hole, homo,
   human, human being, incision, individual, jasper, joint, joker,
   kloof, lad, leak, life, living soul, man, moat, mortal, nose,
   notch, nullah, old boy, one, opening, party, pass, passage, person,
   personage, personality, ravine, rent, rift, rime, rupture,
   scissure, seam, single, slit, slot, somebody, someone, soul, split,
   stud, tellurian, terran, trench, valley, void, wadi, worldling



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

CHAP
       [PPP] Challenge Handshake Authentication Protocol (PPP, RFC
1334/1994)


The Free On-line Dictionary of Computing (30 December 2018):

Challenge-Handshake Authentication Protocol
CHAP

    (CHAP) An
   authentication scheme used by PPP servers to validate the
   identity of the originator of the connection upon connection
   or any time later.

   CHAP applies a three-way handshaking procedure.  After the
   link is established, the server sends a "challenge" message to
   the originator.  The originator responds with a value
   calculated using a one-way hash function.  The server checks
   the response against its own calculation of the expected hash
   value.  If the values match, the authentication is
   acknowledged; otherwise the connection is usually terminated.

   CHAP provides protection against playback attack through the
   use of an incrementally changing identifier and a variable
   challenge value.  The authentication can be repeated any time
   while the connection is open limiting the time of exposure to
   any single attack, and the server is in control of the
   frequency and timing of the challenges.  As a result, CHAP
   provides greater security then PAP.

   CHAP is defined in RFC 1334.

   (1996-03-05)