requiring the great strength of a Hercules; very hard to perform

Digging the tunnel was a herculean task.

having enormous strength, courage, or size.

( initial capital letter ) of or pertaining to Hercules or his labors.

adjective

almighty , backbreaking , colossal , courageous , forceful , gargantuan , gigantic , hard , heroic , huge , impressive , laborious , mighty , strenuous , tough , vigorous , behemoth , brobdingnagian , bunyanesque , cyclopean , elephantine , enormous , gigantesque , immense , jumbo , mammoth , massive , massy , mastodonic , monster , monstrous , monumental , mountainous , prodigious , pythonic , stupendous , titanic , tremendous , vast , giant , muscular , powerful , strong