IPA: /ˌdaɪəˈmɛtrɪkli/
KK: /daɪəˈmɛtrɪkli/
In a way that is completely opposite or contrary to something else.
The two proposals are diametrically opposed to each other.
Diametrically → It is formed from "dia-" (meaning through or across) and "metron" (meaning measure). The word describes something that is directly opposite or across from something else, as in the case of points on a diameter of a circle.
Think of 'across' ('dia-') and 'measure' ('metron') to remember that 'diametrically' refers to something that is directly opposite or across from another point.