lexili seleti: alliance; ally
By - Gootube2000
This is tricky. "donmen" would be curious because it sounds like "ton-men" as you point out, but in spite of that it's best to avoid -men. "-men" doesn't quite fit with the definition anyway, so it might only create confusion as to the meaning and usage of -men. "donmey" might've been an option, but it's also best to avoid -mey. It think this will have to be the first Mandarin word composed of two characters with the -ngu ending.
A priori vowel:
Mandarin, Japanese, Korean, Vietnamese: -o in two-syllable words, and -u in three-syllable words.