Antonyms of adj three-sided

1 sense of three-sided

Sense 1
trilateral, triangular, three-sided -- (having three sides; "a trilateral figure")

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

Similarity of adj three-sided

1 sense of three-sided

Sense 1
trilateral, triangular, three-sided -- (having three sides; "a trilateral figure")
       => multilateral (vs. unilateral), many-sided -- (having many parts or sides)