Speech: Act of speaking
Speech: Formal address to an audience.
Speech: Biological process of speaking.
The word speech operates as a noun in various senses. It's qualified by idiom in terms of its context. Its only real antonym is itself, in an opposed context, or to be 'speechless'. The formal address form of speech is sometimes used as a satiric reference to a statement, implying overstatement or melodrama. The biological usage of the word covers the broader context for related subjects.
Examples of Speech:http://online.sfsu.edu/~kbach/spchacts.html