The Collaborative International Dictionary of English v.0.48:

Lengthways \Length"ways`\ (-w[=a]z`), Lengthwise \Length"wise`\
   (-w[imac]z`), adv.
   In the direction of the length; running or extending in the
   direction of the length of a thing; in a longitudinal
   direction. Contrasted with crosswise.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lengthwise
    adv 1: in the direction of the length; "He cut the paper
           lengthwise" [syn: lengthways, lengthwise, longwise,
           longways, longitudinally]
    adj 1: running or extending in the direction of the length of a
           thing; "the lengthwise dimension" [syn: lengthwise,
           lengthways] [ant: crosswise]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "lengthwise":
   along, at full length, at length, endlong, endways, endwise,
   evenly, flat, flatly, flatways, flatwise, flush, horizontally,
   in length, lengthways, level, longitudinally, longways, longwise,
   on a level