【Irreligious】 , 【unreligious】 ,  【nonreligious】 ,  【ungodly】 ,  【godless】  mean not religious or not devoted to the ends of religion.

【Irreligious】  is not only the most common of the negative forms of religious but the most clearly defined in meaning, for it implies not merely lack of religion but hostility to religion or courses in opposition to it or in violation of its precepts.

It may even suggest impiety, immorality, or blasphemy.

【Unreligious】 , a somewhat uncommon term, implies nothing more than lack of religion; it therefore applies aptly to men, their utterances, or their works and suggests merely the absence of religion or of religious training or religious ideas.

【Nonreligious】  applies not so much to persons as to institutions, activities, projects, and themes for art that are outside the sphere or province of religion or not under the control of a religious body; it therefore comes close in meaning to secular (see under PROFANE 1 ).

【Ungodly】  often comes close to  【irreligious】 , but it carries a stronger suggestion of disobedience to or defiance of divine law.

【Godless】 commonly implies atheism or agnosticism and often definitely implies rejection of religion.