The nasal vowel [ũ] has two graphems as well: um and un. If un / um is followed by a consonant it is pronounced nasale. (This nasal by the way doesn't exist in French. The graphem un / um is not pronounced like an u nasale in French.)
um (un), cumprir (to accomplish)
There is a diphtong as well, but this diphtong is almost irrelevant, because there is only one word where it shows up.