The Catholic Encyclopedia
From the low Latin altaragium, which signified the revenue reserved for the chaplain (altarist or altar-thane) in contradistinction to the income of the parish priest. At present it signifies the fees received by a priest from the laity when discharging any function for them, e.g. at marriages, baptisms, funerals. It is also termed honorarium, stipend, stole-fee.
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Obstat, Nihil. Lafort, Remy, Censor. Entry for 'Altarage'. The Catholic Encyclopedia. https://www.studylight.org/encyclopedias/eng/tce/a/altarage.html. Robert Appleton Company. New York. 1914.