The field "Issue Type" is abbreviated in most issue lists (or issue navigator) as "T". The "Priority" field is abbreviated as "P". But when you're on a form (such as Create Issue), the label for the field is the full name. See screenshot. This makes me think the underlying structure to have a full name and an abbreviated name exists.

Can this be made available for Custom Fields?

Forum message:
https://answers.atlassian.com/questions/196042/abbreviating-headers-in-issue-lists

Previously logged 2 years ago as: JRA-21429, closed with "no you can't, customise Jira source code yourself".