Source : Webster's Revised Unabridged Dictionary (1913)

Linearly \Lin"e*ar*ly\, adv.
   In a linear manner; with lines.

Source : WordNet®

linearly
     adv 1: in a linear manner; "linearly polarized radiation" [ant: {geometrically}]
     2: in a linear fashion; "it grew linearly" [ant: {geometrically}]