The term "most warrantable" refers to something that is very justifiable or defensible. Its antonyms include unjustifiable, indefensible, untenable, unfounded, baseless, and unreasonable. The word "unjustifiable" means lacking in justification or having no valid reason or excuse. "Indefensible" is used to describe something that cannot be justified or defended. "Unreasonable" describes something that is unjustifiable or implausible. "Untenable" refers to something that cannot be supported or maintained. "Baseless" indicates that something is not supported by any evidence or facts. In contrast to "most warrantable," these antonyms suggest that something lacks a solid justification or a sound argument.