What is the antonym of 'Cardinal'?

Cardinal (adjective): 
English Meaning: Serving as an essential component. a cardinal rule.
Bangla Meaning: প্রধান; মুখ্য; অগ্রগণ্য; অপরিহার্য: the cardinal virtues.

Synonyms: Fundamental (মৌলিক), Chief (প্রধান), Paramount (সর্বোচ্চ), Central (কেন্দ্রীয়), Dominant (প্রভাবশালী)। 
Antonyms: Unimportant (কম গুরুত্বপূর্ণ), inessential (অপরিহার্য নয় এমন), Auxiliary, (সহায়ক) Unmercenary (অপ্রয়োজনীয়), Least (ন্যুনতম)।
Other Forms:
- Cardinal (Noun) (Roman Catholic Church) one of a group of more than 100 prominent bishops in the Sacred College who advise the Pope and elect new Popes. 
- The number of elements in a mathematical set; denotes a quantity but not the order
Example Sentence: 
1. One of the most popular presidents in recent memory is about to commit a cardinal sin.
2. My cardinal rule is to always be honest. 

Source: Website lecture.