1530s "of or pertaining to the gospel" (adj.), also "a Protestant," especially a German one (n.); with -al (1) + evangelic (early 15c.), from Old French evangelique, from Late Latin evangelicus, from evangelista (see evangelist).

From mid-18c. in reference to a tendency or school in Protestantism seeking to promote conversion and emphasizing salvation by faith, the sacrifice of Christ, and a strictly religious life. As "member of the 'evangelical' party in a church" from 1804. Related: Evangelically; Evangelicalism (1812).

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Definitions of evangelical from WordNet

evangelical (adj.)
relating to or being a Christian church believing in personal conversion and the inerrancy of the Bible especially the 4 Gospels;
evangelical Christianity
an ultraconservative evangelical message
evangelical (adj.)
of or pertaining to or in keeping with the Christian gospel especially as in the first 4 books of the New Testament;
evangelical (adj.)
marked by ardent or zealous enthusiasm for a cause;
Synonyms: evangelistic