The Collaborative International Dictionary of English v.0.48:

Skyscraper \Sky"scrap`er\, n.
   (a) (Naut.) (1) A skysail of a triangular form. [Rare] (2) A
       name for the one of the fancy sails alleged to have been
       sometimes set above the skysail. [Obs.]
   (b) A very tall building, especially one over 20 stories
       high.
   (c) Hence, anything usually large, high, or excessive. [Slang
       or Colloq.]
       [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

skyscraper
    n 1: a very tall building with many stories

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "skyscraper":
   antenna tower, architecture, barbican, belfry, bell tower,
   building, campanile, casa, cliff dwelling, colossus, column,
   construct, construction, consulate, country house, country seat,
   cupola, dacha, deanery, derrick, dome, dwelling house, edifice,
   embassy, erection, establishment, fabric, farm, farmhouse,
   fire tower, hall, house, houseboat, lake dwelling, lantern,
   lighthouse, living machine, lodge, manor house, manse, martello,
   martello tower, mast, minaret, monument, obelisk,
   observation tower, packaged house, pagoda, parsonage, penthouse,
   pilaster, pile, pillar, pinnacle, pole, prefab,
   prefabricated house, prefabrication, presidential palace, pylon,
   pyramid, ranch house, rectory, roof, shaft, sod house, spire,
   split-level, standpipe, steeple, structure, stupa, superstructure,
   television mast, tope, tour, tower, town house, turret, vicarage,
   water tower, windmill tower