O is for oma, opa and oksel.
Oma is granny and opa is grandpa, so very useful words to know. I think these were one of the first words both my parents and my parents-in-law learnt in Dutch.
Oksel is armpit, which is a word I find amusing. In both languages. At least in English it’s descriptive so you can guess where it means, even if you don’t know it.