'missionary-supporting' is a compound of 'missionary' and 'supporting'. 'missionary' originates from Late Latin, specifically the word 'missionarius', where 'missio' meant 'a sending' (from Latin 'mittere', 'to send'). 'supporting' originates from Old French 'soutenir', ultimately from Latin elements 'sub-' and 'tenere' where 'sub-' meant 'under' and 'tenere' meant 'to hold'.

'missionary' changed from Late/Medieval Latin 'missionarius' into Middle English forms (e.g. 'missionarie') and eventually became the modern English 'missionary'. 'support' passed into English via Old French 'soutenir' (and related Old French forms) and Middle English, evolving into the modern verb and the present participle 'supporting'; the compound form arose by combining the two words in modern English to describe support given to missionaries.

Initially, 'missionary' primarily meant 'one sent' (a person sent on a mission); over time it narrowed to mean specifically a person sent to promote religious faith. 'Support' originally emphasized physical holding or sustaining; it broadened to include financial, logistical, moral, and institutional assistance—so 'missionary-supporting' now commonly means providing such assistance to missionary activity.