Definition of "one-dimensional"

one-dimensional

adjective
comparative more one-dimensional, superlative most one-dimensional
1. Having length, but no width, height or depth.
2. (figuratively) Lacking depth or believability; flat.
  Quotations
  Such one-dimensional characters have always existed in the theatre along with more recognizably human characters.
  1972, Hardie Albright, Stage direction in transition
  In contrast to this are the flat, one-dimensional characters found in fables.
  1999, Kimberly Kimbell-Lopez, Connecting with traditional literature
3. (figuratively) Lacking personal depth and substance; conceited, vain, shallow, superficial.