A person who is partially or half-devoted to a religious faith, cause, or pursuit; a lukewarm follower or believer.
From 'demi-' (half) + 'votary' (a devoted follower), where 'votary' comes from Latin 'votum' (a vow or wish). The prefix 'demi-' indicates incompleteness or partial commitment.
Shakespeare and other Renaissance writers used 'demivotary' to describe people who were wishy-washy about their beliefs—it's basically the original word for someone who's 'spiritual but not religious'!
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