"[...] and there being no one for her to talk to but her maids and the chaplain—a clumsy man deep in his books [...]"[1]
A chaplain is "a priest or other Christian minister who is responsible for the religious needs of people in a prison, hospital, etc. or in the armed forces."[2] In the case of "The Duchess at Prayer", the chaplain provides religious services for the secluded villa's inhabitants.
[1] Wharton 1901, p. 8
[2] see Hornby 2019, Nr. 12