Substitutes for words can be found using a dictionary or thesaurus. Dictionary entries often include cross-references to synonymous or closely related words. Definitions may provide good word substitutes within the description itself.
A thesaurus is a reference work that lists words in groups according to the similarity of their meaning. Occasionally, antonyms form part of this list. Care must be taken to avoid substitutes that do not work in the same context. For example, potential substitutes for the word "tired" include drained, fatigued and stale. However, it is unlikely that "stale" could be used effectively as an adjective to describe a person's state of well-being.