615: sloth and month Aug 14, 2016

There are plenty of suffixes in English that turn adjectives into nouns, including commonly '-ness' and '-ity'. Older, Germanic words may occasionally have the '-th' ending, such as how 'wide' turns to 'width', 'warm' turns to 'warmth' and interestingly, 'moon' turned to 'month' because months went by moon-cycle. These endings are a bit rare, and often people won't notice if someone says 'deepness' instead of 'depth'. The quality of being slow, could be 'slowness' as well, but traditionally it is 'sloth'. When Europeans found the animal sloths, remarking upon the slow nature of the animal, names then after their speed.
For more information on suffixes, click here.