A more thorough explanation:

QUIA ALIMENTA LIBERIS NON DEBENTUR NISI IN SUBSIDIUM

Because aliment (alimony) is not due to children except in aid. A parent was not required to support a child for whom another source, such as a separate estate, provided.

This term is used in Scots law and means that a parent is not obligated to provide financial support to their child if another source, such as a separate estate, is already providing for them. In other words, a parent is only required to provide financial support to their child if no other source is available to do so.

For example, if a child's grandparents have set up a trust fund for them, the child's parent may not be required to provide financial support to the child because the trust fund is already providing for them. However, if the trust fund runs out of money or is no longer available, the parent may then be required to provide financial support to the child.