Never remove any of the notes that are to be altered, else it will not be the chord that is called for. In eleventh chords the 9 can be removed. Never remove the 1, for it will completely change the chords property. Dominant chords are often with D or no letter at all, such as D7 or 7. Major seventh chords are written as M7, sometime the 7 will have a slash through it.
Tertiary chords are chords built with stacked thirds.
Quartal chords are built with stacked fourths. Quintal chords are built with stacked fifths. Chords Clusters are stacked seconds. These seconds can be major or minor, diminished is not normally used because it sounds like a unison and the augmented gives the sound of a third. Chords built from seconds do not have traditional names, such as those built with thirds.