"full of ardor," 1770, perhaps a variant of arduous with overtones of ardor. Useful only to poets, and, as it is first attested in Chatterton, perhaps a faux medievalism.
Entries linking to ardurous
arduous adj.
1530s, "hard to accomplish, difficult to do, attended with much labor," from Latin arduus "high, steep," also figuratively, "difficult, hard to reach" (from PIE root *eredh- "high;" for which see ortho-). The literal sense of "high, steep, difficult to climb" is attested in English from 1709. Related: Arduously; arduousness.
What is arduous requires more energy and endurance, and is less within the reach of common powers, than what is hard. Its primitive meaning of steep climbing is still felt in it, and makes it suggestive of severe and protracted effort. [Century Dictionary]
ardor n.
"heat of passion or desire," mid-15c., ardour, from Old French ardure "heat, glow; inflammation; passion" (12c., Modern French ardeur), from Latin ardorem (nominative ardor) "a flame, fire, burning, heat;" also of feelings, etc., "eagerness, zeal," from ardere "to burn" (from PIE root *as- "to burn, glow"). In Middle English used of base passions; since Milton's time of noble ones.