Well, I consider anything post 500AD modern times.
   While it's nice that:
   c. 1200, "state of life bound by monastic vows," also "conduct
   indicating a belief in a divine power," from Anglo-French
   religiun (11c.),

   relates well to our current understanding,

   religare - to bind LATIN
   religio - obligation, bond, reverence LATIN

   are more general.

   Example: reverence for the Scientific method is "religio".
   Obligation / bond / bind - would be people who work within the
   Sciences and are ethnically bound to follow the precepts.

   ie: Religion.

   The current form didn't seem to start getting used 'til around
   11c AD - definitely modern times. Christiandom had already been
   around 1000 years by then: a VERY long time indeed.