Antonyms for the word "unsuitable" include "appropriate," "suitable," "fitting," "proper," "adequate," "acceptable," "compatible," and "fitting." "Appropriate" denotes something that is suitable for a specific occasion or purpose, while "suitable" suggests something that is appropriate for a particular situation. "Fitting" implies that something is perfect or appropriate for a particular purpose or occasion. "Proper" refers to something that is suitable according to what is socially acceptable, moral or ethical standards. "Compatible" suggests that something is well suited or designed to work well together. Finally, "adequate" refers to something that is sufficient or enough.