The spell check keeps trying to change ‘clowder’ to ‘chowder’, which I don’t think anyone would want made of cats.

According to the only reference I could find, ‘clowder’ is related to ‘clutter’, and another collective noun for cats is ‘glaring’.  Imagine yourself cornered in a dead-end with a half dozen alley cats glaring at you, because you inadvertently stepped near their favourite mouse deli.  Perhaps, then, a ‘hissing’ of cats?

The collective noun for kittens, I learn, is ‘kindle’.  I wonder if the marketing people knew that when they named a certain electronic book reader.