The antonyms for the word "un flexible" include "flexible," "pliant," "supple," "yielding," "bendable," "elastic," "malleable," and "adaptable." Being "flexible" means to be capable of bending and adapting to new situations, while "pliant" suggests suppleness and ease of movement. "Supple" implies fluidity and smoothness, while "yielding" means to be accommodating and willing to compromise. "Bendable" and "elastic" both suggest the ability to bend and flex but with different degrees of stiffness. "Malleable" describes something that can be shaped or molded easily, and "adaptable" suggests being able to adjust to changing circumstances.