"knee"

Translation: genunchi

[Schattenparker]

can be either genunchi or genunche in both singular and plural, but the other forms depend on that choice which makes this noun either masculin or neuter, see
https://dexonline.ro/definitie/genunchi#paradigmTab (tab declinări)

[Luchtmens]

Good observation, but everyone uses the masculine noun with identical singular and plural forms: un genunchi, doi genunchi.

Many people would even tell you "genunche" is a mistake (in either singular or plural). There was a notorious case when the Romanian minister of Education posted an update on his health situation on social media which went like this: Totul este sub control, am ieşit din operaţia la genunche. Needless to say, he has been mocked ever since and dubbed ministrul "genunche".

The thing is, dexonline is a complete reference, but it may not always give you a gist of the modern/ common language. I recommend using this dictionary when you are not sure about the right or preferred word form or paradigm. This is the ultimate book on correct writing in modern Romanian.

[Schattenparker]

Thank you! Here that link again, for those hyperlinks do not work in the (Android?) app:
https://diacritica.files.wordpress.com/2010/04/doom2.pdf

(and since you do German: das Knie (Sing), die Kni-e (Plur) is spelled the same but is pronounced (by most Germans) differently - it is a confusing word as to Sing./Plur. in German, too...)

[Luchtmens]

Thanks for posting the link (I didn't notice hypertext doesn't work in the app...).

I used to pronounce Knie the same way in sg. and pl., you shed some light on it.

[Schattenparker]

das chniii, diii chniiă :-)