Andy-Hughes
/// The term 'devout' indicates a deep-seated religious feeling, whereas atheism is the absence of such belief. ///
It also as other meanings, take your pick.
*** totally committed to a cause or belief. ***
That could mean totally committed to atheism.
"the most devout environmentalist"
the most devout atheist.
dedicated atheist
a committed atheist.
staunch atheist.
Got the gist? Take your pick of some others.
synonyms: dedicated, devoted, committed, loyal, faithful, staunch, genuine, firm, steadfast, resolute, unwavering, sincere, wholehearted, keen, earnest, enthusiastic, zealous, passionate, ardent, fervent, intense, vehement, active, sworn, pledged;