Sentence:  ‘You′ve already spent a <WSD>bomb</WSD>!' / ‘Not "on" it, Sal — "under" it. Presents!' As we eventually staggered up to bed, Sally said to me, ‘I hope to God he′s not been spending a <WSD>bomb</WSD> on presents, too....' 
Meaning of the word marked with <WSD> tags:  A large amount of money.