Source : Webster's Revised Unabridged Dictionary (1913)

Collateral \Col*lat"er*al\, a. [LL. collateralis; col- +
   lateralis lateral. See {Lateral}.]
   1. Coming from, being on, or directed toward, the side; as,
      collateral pressure. ``Collateral light.'' --Shak.

   2. Acting in an indirect way.

            If by direct or by collateral hand They find us
            touched, we will our kingdom give . . . To you in
            satisfaction.                         --Shak.

   3. Related to, but not strictly a part of, the main thing or
      matter under consideration; hence, subordinate; not chief
      or principal; as, collateral interest; collateral issues.

            That he [Attebury] was altogether in the wrong on
            the main question, and on all the collateral
            questions springing out of it, . . . is true.
                                                  --Macaulay.

   4. Tending toward the same conclusion or result as something
      else; additional; as, collateral evidence.

            Yet the attempt may give Collateral interest to this
            homely tale.                          --Wordsworth.

   5. (Genealogy) Descending from the same stock or ancestor,
      but not in the same line or branch or one from the other;
      -- opposed to lineal.

   Note: Lineal descendants proceed one from another in a direct
         line; collateral relations spring from a common
         ancestor, but from different branches of that common
         stirps or stock. Thus the children of brothers are
         collateral relations, having different fathers, but a
         common grandfather. --Blackstone.

Collateral \Col*lat"er*al\, n.
   1. A collateral relative. --Ayliffe.

   2. Collateral security; that which is pledged or deposited as
      collateral security.

Source : WordNet®

collateral
     adj 1: descended from a common ancestor but through different
            lines; "cousins are collateral relatives"; "an
            indirect descendant of the Stuarts" [syn: {indirect}]
            [ant: {lineal}]
     2: serving to support or corroborate; "collateral evidence"
        [syn: {confirmative}, {confirming}, {confirmatory}, {corroborative},
         {corroboratory}, {substantiating}, {substantiative}, {validating},
         {validatory}, {verificatory}, {verifying}]
     3: accompaniment to something else; "collateral target damage
        from a bombing run"
     4: situated or running side by side; "collateral ridges of
        mountains"

collateral
     n : a security pledged for the repayment of a loan