Which kind of parts of speech is the word 'Vital'?

• Vital: [adjective]
English meaning: necessary for the success or continued existence of something; extremely important.
Bangla meaning: জীবনসম্পৃক্ত; জীবনসম্বন্ধীয়; জীবনের জন্য অপরিহার্য; জৈবনিক; জীবনীয়; জীবনসাধক।

Example: A strong opposition is vital to a healthy democracy.

Source: CAmbridge & Accessible Dictionary.