Source : Webster's Revised Unabridged Dictionary (1913)

Whapping \Whap"ping\, Whopping \Whop"ping\, a.
   Very large; monstrous; astonishing; as, a whapping story.
   [Colloq.]

Source : WordNet®

whopping
     adj : (used informally) very large; "a thumping loss" [syn: {humongous},
            {banging}, {thumping}, {walloping}]
     adv : extremely; "they all were whopping drunk"

whop
     v 1: hit hard; "The teacher whacked the boy" [syn: {whack}, {wham},
           {wallop}]
     2: hit hard [syn: {sock}, {bop}, {whap}, {bonk}, {bash}]
     [also: {whopping}, {whopped}]

whopping
     See {whop}