with a capital [A etc.]
with 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.
See also: capital