The phrase "speaks one piece" refers to someone who speaks honestly and truthfully, without hiding any information. Antonyms for this phrase could be someone who speaks in a dishonest or deceptive manner, concealing important facts or twisting the truth. Words like "deceitful," "untruthful," and "dishonest" could be used as antonyms for "speaks one piece." Other antonyms include "dissembling," "phony," "fake," and "disingenuous." Such individuals are often referred to as "liars" or "fakers" who cannot be trusted. In contrast, "speaks one piece" individuals are respected for their integrity and honesty.