Regularly disappearing in nature, or into prayer (7)
I believe the answer is:
introit
'prayer' is the definition.
(I've seen this before)
'regularly disappearing in nature or into' is the wordplay.
'regularly disappearing' means one should take alternating letters (letters removed at regular intervals).
'in'+'nature'+'or'+'into'='innatureorinto'
The alternating letters of 'innatureorinto' are 'INTROIT'.
(Other definitions for introit that I've seen before include "Pre-Eucharist prayer" , "Antiphon" , "Introductory anthem" , "Opening hymn" , "Church psalm" .)