Dictionary.com defines secular as “not pertaining to or connected with religion.” Hence, an opposite word would be sacred. The etymology of the word is Latin. Saeculum means “age” or “generation.” Secondly, saecularis means “once in an age” or “worldly.” The word is an adjective.
The noun secularity is the condition of being unrelated to religion. However, it is not to be mistaken with atheism. Further, Secularism is a theory of saying that the state should be separate from religion. So, secularization is a process of making a secular state.
Atheism is the rejection of the existence of a god or multiple gods. To be secular means to separate public affairs from religion. It usually offers greater freedom of religion and is a cornerstone of western democracies.