What is the term for seizing and holding something firmly?

The term that best fits the definition of seizing and holding something firmly is "grasp." Grasping implies a secure grip that involves both holding onto something strongly and having a good understanding of it. This term encompasses both physical and abstract interpretations, making it versatile in usage.

"Clutch" also conveys a sense of holding tightly but often implies a sense of urgency or fear, which may not always align with the steady use of "grasp." "Capture" typically refers to taking possession of something, often in a more metaphorical or forceful sense, such as capturing an idea or capturing someone in a physical or legal context, rather than just holding something firmly. "Snatch" suggests a quick, sudden grab that lacks the firmness implied in the term "grasp," often with a connotation of being forceful or taking something without permission.

In summary, "grasp" accurately conveys the action of holding something firmly, capturing its essence more effectively than the other options.