Plural of boatload; large quantities or numbers, as much as a boat can carry, or figuratively, a large amount of something.
Compound noun from 'boat' plus 'load,' pluralized with '-s.' Originally literal (the capacity of a boat), now often used figuratively to mean 'a lot of.'
Notice how 'boatloads' has gone almost entirely metaphorical in modern usage: 'boatloads of money,' 'boatloads of complaints.' We're using a maritime measurement to describe abstract quantities—which reveals how metaphor structures how we think about excess.
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