From the Latin root gradus/gradi, meaning to step, walk, or move.

Untitled Poem

To regress is to travel back
  as is to retrogress, you know.
To egress is to leave a lack
  of you, as you do outward go.

Moving toward was once aggression
  since the Latin “‍ag‍” means “‍to‍”;
but agress’s new suggestion
  is a violent thing to do.

That which moves into ingresses
  so it’s an ingredient;
that which moves ahead progresses
  but there’s no “‍progredient.‍”

Digressions move apart (from what
  is usually unspecified);
Transgressions move across (to cut
  across a boundary is implied).

To congress is to move with others
  though our congress rarely does;
most’s votes are canceled by another’s:
  the “‍with‍”, I fear, just never was.