The word up for consideration today is one we all use regularly to mean ‘bad’ or ‘poor’ without ever really considering what it originally meant. But stop and think about it and it seems obvious. The word is lousy. Break it down and it clearly comes from louse.
Louse itself existed in Old English as lus which goes back further to Proto-Indo-European *lus-. It’s hardly surprising that louse should date back this far; in our modern, hyper-hygienic time, lice are rarely a problem but through most of our history the insects were a familiar pest.
The extension of the meaning of lousy from ‘infested with lice’ to ‘poor’ is pretty transparent and it happened in an impressively short period: between the middle and the end of the 14th century.
So in 1377, the former meaning was used and understood in William Langland’s poem Piers Plowman:
With an hode on his hed a lousi hatte aboue.
(With a hood on his head, a lousy hat above.)
But Chaucer was able to use the latter meaning in Friar’s Tale, sometime after 1387:
A lowsy jogelour kan deceyve thee.
(A lousy juggler can deceive you.)
Lousy developed another meaning in American English in the mid-19th century, that of ‘swarming with’ or ‘full of’. Oxford Dictionaries gives the example:
‘The town is lousy with tourists.’
Fortunately for us, we don’t have much use for the original sense of the word any more. The nice thing about it, though, is that the spelling and pronunciation have barely changed so the etymology is apparent and doesn’t involve lots of research and guesswork.