disciplino

Not dis- plus anything. Esperanto really does have a dis- prefix meaning apart or in all directions - disdoni, to hand out; disiri, to go separate ways - and it makes the front of this word look like a seam. It is not one. There is no root ciplin-, and scattering has nothing to do with the meaning. The word came in whole from Latin, the way diskreta did at rank 2,708, and both are worth noticing together because they are the same trap sprung twice in one course.

Both senses are standard. PIV gives disciplino its two jobs and Esperanto keeps them apart with no strain, because the contexts never overlap. The first is order enforced or self-imposed: armea disciplino, labori kun disciplino, memdisciplino for the version you apply to yourself. The second is a field of knowledge: la disciplino de la lingvistiko. Nothing in the word chooses between them, which is normal for an international borrowing and slightly un-Esperanto for a language that likes one piece to one meaning.

Where it ends and fako begins. Fako at rank 1,369 is the everyday word for a compartment, a department, a specialism - your fako at a university is the department you sit in, and fakulo is the expert. Disciplino in the second sense is the more academic word for the subject as an organised body of knowledge, and it carries a faint suggestion of rigour that fako does not. If you are unsure, use fako: it is commoner, older in the language, and never wrong for a subject area. Save disciplino for when you mean the discipline of a discipline.