Religious
A standard definition:
pertaining to, or concerned with, or in accordance with the principles of a religion;
In a religious naturalist context:
actively interested in or caring about, considering, and acting upon themes and questions that have been considered by traditional religions, as in forming a worldview (how things are; what things matter; what is right and just and good) and trying to live in accordance with values
As described by John Dewey (distinguishing between a religion and the religious):
a felt quality of unity and purpose within the finite experiences that we have
Religion
(derived from the Latin, religare, to fasten or bind)
a personal set or institutionalized system of beliefs concerning the cause, nature, and purpose of the universe, usually involving ritual observances and often containing a moral code; usually includes, but does not require, belief in and reverence for a creative force or creator
Spiritual
pertaining to spirit (as in a life-force or the essential quality in beings or phenomena); use to distinguish interest in sacred matters from a secular orientation; (while “spiritual” and “religious” are similar in many ways, the connotation of “spiritual” is mainly individual, while “religious” suggests connection to the teachings of specific traditions or institutions)
Secular
(from the Latin saeculum, the present world) relating to the worldly or temporal; not overtly religious
Atheist
one who does not believe in or denies the existence of God
Transcendent
lying beyond the limits of ordinary or material experience; beyond comprehension
Numinous
containing and conveying a sense of the presence of a mysterious spiritual power
Sacred
expressing the essence of the ultimate force/source of creation; deserving of veneration and awe
Divine
related to, proceeding from, or having qualities attributable to a god
Holy
venerated as sacred, worthy of devotion
Reverent
expressing (or characterized by) profound adoring awed respect
Pious
showing reverence for and devotion to worship
Devout
devoted to religion or religious observance