/ ɪnˈfɜːnl; NAmE ɪnˈfɜːrnl/ adjective
1.
[ only before noun ] ( old-fashioned ) extremely annoying :
Stop that infernal noise!
2.
( literary ) connected with hell
► in·fer·nal·ly / -nəli; NAmE / adverb
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WORD ORIGIN
late Middle English : from Old French , from Christian Latin infernalis , from Latin infernus below, underground, used by Christians to mean hell, on the pattern of inferni (masculine plural) the shades and inferna (neuter plural) the lower regions.