"diminished" gets brought up only when discussing chords and intervals it seems, "flat" is a modifier to a note and nothing more. however, diminishing an interval means making one note flat, that's why it gets so confusing.  when we say Cdim we mean C/Eb/Gb. When we say Cdim7 is the seventh also diminished (C/Eb/Gb/Bbb=A)?
yes