大 (dà): Big, great, noble. Here it elevates the concept to a higher level.
义 (yì): Justice, righteousness, moral principle. This is the core of the idiom.
凛 (lǐn): Awe-inspiring, stern, severe. It describes the intimidating and respectable aura of the person.
然 (rán): A grammatical suffix meaning “in the manner of…” or “-ly,” which turns the preceding characters into a descriptive phrase.
When combined, 大义凛然 literally means “in the manner of (然) awe-inspiring (凛) great justice (大义).” The characters paint a vivid picture of a person whose commitment to a noble, just cause is so powerful that it makes them appear stern, imposing, and profoundly respectable.