Antonyms of adj four-sided

1 sense of four-sided

Sense 1
quadrilateral, four-sided -- (having four sides)

INDIRECT (VIA multilateral) -> unilateral, one-sided -- (involving only one part or side; "unilateral paralysis"; "a unilateral decision")

Similarity of adj four-sided

1 sense of four-sided

Sense 1
quadrilateral, four-sided -- (having four sides)
       => multilateral (vs. unilateral), many-sided -- (having many parts or sides)