Quote Originally Posted by bitpicker View Post
Isn't it possible that some or even all of these words used to be formed as augmentatives and just lost the connection to the basic word?
No, mostly not. There are other meanings of this suffix, which are almost lost in time. Suffix -ище had meaning "a place for" (something or doing something) and produces neuter noun. So we have words like стойбище, пастбище, лежбище, убежище, кладбище (from verbs) топорище, голенище, огнище (from nouns) и т.д.


Quote Originally Posted by bitpicker View Post
And does the former translate to "very smart large cat"? The second I don't get at all...
Very cunning large cat. As for second, there is a way of speaking: when someone with усы (mustache or whisker) makes some sound (like hisses) with his mouth, it can be described as "шипит в усы".

BTW котище does not necessarily mean very large cat. The cat may be just very prominent in some sense. A special cat. Impressive. This is true about this suffix in general. But by default it means "very large".