There are many synonyms for the word "big." Some of the most common ones include:

• Colossal
• Considerable
• Enormous
• Fat
• Full
• Gigantic
• Hefty
• Huge
• Immense
• Massive
• Sizable
• Substantial
• Tremendous
• Vast

These synonyms can be used to describe something that is of great size, weight, number, or capacity, or something that has great significance or lasting effect.