Equivocation

Equivocation is a logical fallacy that involves taking a word with more than one definition and freely substituting one definition for another.

For example:
 * "A feather is light. Therefore, a feather cannot be dark."
 * There are two meanings of the word light. The first sentence assumes a meaning that is the opposite of heavy, not the opposite of dark.

This fallacy is used frequently in the service of apologetics arguments. A few relevant examples:
 * 1) Atheism is based on faith.
 * 2) * There are multiple meanings of the word faith, for example things you trust in without critical analysis or things which people believe with good evidence.
 * 3) Prayer is meditation.
 * 4) * Redefining prayer as only a form of mental meditation rather than petitions for things is often used to justify the efficacy of prayer in the petition context.
 * 5) "No true Scotsman" fallacy.
 * 6) * When someone says, "That person wasn't really a Christian because he did that," they are relying on ambiguity in the word Christian and redefining it to suit their needs.
 * 7) The existence of laws implies a law-giver.
 * 8) * This stems from a confusion between natural laws and legal laws. Even legal laws do not always require a law giver. Common law can involve customs which are Memes that evolved over time.
 * 9) Evolution is only a theory.
 * 10) * This plays on the confusion between the scientific and colloquial definitions of the word theory.