Meaning

adjective rejecting any belief in gods

adjective holding that only material phenomena can be known and knowledge of spiritual matters or ultimate causes is impossible

adjective denying or questioning the tenets of especially a religion

originEtymology tree Proto-Indo-European *né Proto-Indo-European *n̥- Proto-Germanic *un- Proto-West Germanic *un- Old English un- Middle English un- English un- English believing English unbelieving From un- + believing.

Etymology from Wiktionary, CC BY-SA 3.0