Important synonyms vary in nuance and context, but commonly used replacements include:

• Significant – best for "of great meaning or lasting effect" (e.g., "a significant breakthrough").

• Crucial – emphasizes essentiality, often for decisions or outcomes (e.g., "a crucial moment").

• Vital – implies necessity for survival or success (e.g., "vital to the project’s success").

• Major – used for large scale or importance (e.g., "a major achievement").

• Pivotal – highlights a turning point or decisive role (e.g., "a pivotal discovery").

• Eminent – often describes respected or distinguished individuals (e.g., "an eminent scientist").

• Foremost – used for the most important or leading position (e.g., "foremost expert in the field").

• Essential – stresses indispensability (e.g., "essential for progress").

These synonyms are context-dependent: use significant or crucial for general importance, eminent or foremost for people, and vital or essential when something is indispensable. Avoid informal terms like "big" in academic or formal writing.