Idiom
with a capital Awith a capital [A/B/C etc.]
1.
something that you say in order to emphasize a particular quality.
You're trouble with a capital T, you are!
2.
if you talk about a subject with a capital A/B/C etc., you mean the most formal and often limited understanding of that subject.
The Academy has been criticized for being too traditional and only supporting Art with a capital A.