Oom-Lout in Germanic Languages

Oom-lout is when a vowel changes its location in that nice little vowel triangle or vowel rhombus. In Germanic languages like English, it's usually describing moving from back to front. That's likely why you know a lot of the irregular plurals in English are very, very common word words. Other Germanic languages also have a, a oom- lout and u oom-l out which gives you the horrible mess of Icelandic noun declensions.