The Collaborative International Dictionary of English v.0.48:

Sidelong \Side"long`\, adv. [See Sideling, adv.]
   1. Laterally; obliquely; in the direction of the side.
      [1913 Webster]

   2. On the side; as, to lay a thing sidelong.

   Note: [See Sideling, adv. ] --Evelyn.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sidelong \Side"long`\, a.
   Lateral; oblique; not being directly in front; as, a sidelong
   glance.
   [1913 Webster]

         The bashful virgin's sidelong looks of love.
                                                  --Goldsmith.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sidelong
    adv 1: on the side; "the plow lay sidelong on the ground"
    2: with the side toward someone or something; "seated sidelong
       to the window"- Nathaniel Hawthorne
    3: to, toward or at one side; "darting eyes looking sidelong out
       of a wizened face" [syn: sidelong, sideways, obliquely]
    adj 1: (used especially of glances) directed to one side with or
           as if with doubt or suspicion or envy; "her eyes with
           their misted askance look"- Elizabeth Bowen; "sidelong
           glances" [syn: askance, askant, asquint, squint,
           squint-eyed, squinty, sidelong]
    2: situated at or extending to the side; "the lateral branches
       of a tree"; "shot out sidelong boughs"- Tennyson [syn:
       lateral, sidelong]
    3: inclining or directed to one side; "moved downward in a
       sidelong way" - Bram Stoker