Shamelessly stolen from
goofy's blog: I knew that there are a handful of abstract nouns of quality ending in
-th that typically derive from adjectives, but I learned a couple new ones.
Strong/strength,
long/length,
wide/width,
deep/depth, and
broad/breadth are probably the most familiar and obviously related pairs.
High/height is a bit of an oddball—the final
-th dissimilated from the preceding
gh and became
-t, and the vowel ended up the same because of analogy with
high (though the spelling reflects the older pronunciation of the vowel). The form
heighth is a nonstandard variant that retained the original ending.
Whole and
health are not terribly obvious unless you know that the
w in
whole is unetymological and was mistakenly added later. Also, the meaning of
whole has broadened and drifted somewhat, but
hale, which is the same word descended from a different dialect of Old English, has preserved the meaning of "healthy".
Slow/sloth is another slightly odd pair, because the original noun form was
sleuth (not related to the modern word
sleuth). The form
sloth is a formation from Middle English without the vowel change.
Dear/dearth and
weal/wealth are a little more obvious, but
merry/mirth and
foul/filth were new to me. And apparently
dry/drought are part of the series, too, with the same change to
-t that
height had. But what I don't get about that pair is the vowels. The
-th suffix typically causes umlaut (or fronting) and shortening of the stem vowel, but here we seem to have the opposite: the root word has an umlaut, and the
-th noun doesn't. Perhaps a better etymologist than I could explain it.
