I think I might have mentioned a few words from this series before, but I don't know if I've ever dug into the whole thing.
In Proto-Germanic there was a suffix -itho that was used to form nouns from verbs or adjectives. In English it typically became -th, but it usually became -t after a fricative (like /f/, /s/, or /x/, the sound in words like loch or Bach). It's obvious that give and gift are related and that long/length, wide/width and others like them are related, but some other pairs may be less obvious, like drive/drift (the act of driving or a thing that has been driven), weave/weft, and slow/sloth. It also might not be obvious that the -t and the -th are the same suffix and that it was used so extensively, especially since it's not a productive suffix today.
Here are all the pairs I've found:
strong/strength
long/length
wide/width
high/height
weigh/weight
broad/breadth
deep/depth
warm/warmth
grow/growth
true/truth/troth
whole/health
bear/birth/berth
weal/wealth
foul/filth
rue/ruth (now only found in ruthless)
dear/dearth (because when something is scarce, it becomes dear, that is, expensive)
dry/drought
draw/draught/draft
mow/math (as in aftermath, literally the grass that grows after the first crop of hay is cut)
wroth/wrath (the -th in the suffix assimilated)
young/youth
die/death
see/sight
fly/flight
heave/heft
steal/stealth
thrive/thrift
slay/slaught (which has been displaced by slaughter, a doublet from Old Norse)
sly/sleight
thief/thieve/theft
shrive/shrift
freeze/frost (the OED says it belongs here, but Etymonline.com and Wiktionary don't seem to agree)
merry/mirth
may/might (in this case the noun meaning 'strength'; the verb might comes from the past participle)
think/thought (again, the noun, though the past tense and past participle of the verb look the same)
??/thirst (apparently it has the same suffix, but the original stem has not survived)
??/oath
??/bath (the OED says these last two also have the suffix, but Etymonline.com and Wiktionary don't seem to concur, and it looks like the stems haven't survived)
The vowel change in many of these suffixed words comes from the original form of the suffix, -itho. /i/ is a front vowel, and it often triggered umlaut (that is, vowel fronting) in vowels in preceding syllables in Germanic languages. The /i/ later disappeared (along with the final /o/), leaving only the umlaut as evidence that it existed.
But many of these words were formed later, after the umlaut had occurred and the /i/ dropped out, so some of them are modeled on existing pairs, while others just slapped the -th/-t on the end without regard to the vowel. But the suffix stopped being productive altogether (except for some jocular formations like coolth) sometime in Middle English, so we're just left with all these pairs that we might not even recognize as pairs, let alone as a regular pattern of word formation that goes back over two thousand years.