Living, livelihood, subsistence, sustenance, maintenance, support, keep, bread, bread and butter are comparable when they denote the means, especially the amount of money or goods, required to keep one supplied with the necessities of life (as food, housing, and clothing) and sometimes also the nonessentials that with the necessities supply the needs of a full life.
Living is perhaps the most general term since it may denote either the necessities and provisions with which one supports life or the income with which these may be obtained.
Typically it is used in a few simple idioms; thus, a man usually earns or makes or gets a or his living; he does something (as writing, spinning, or farming) for a or his living; someone or something owes or provides him a living.
Livelihood may be indistinguishable in meaning from living, but unlike the latter it may apply specifically to the means (as a trade, profession, or craft) by which one earns a living.
Subsistence may be a close synonym of living, but often it more specifically denotes means sufficient merely to maintain life and implies an amount of money or supply of goods that provides a person or his family with no more than basic necessities (as of housing, food, and clothing).
Sustenance is often used in place of living when the emphasis is upon the food that is necessary not only to one's existence but to one's well-being. But it is also often used to imply all the necessaries of life.
Maintenance usually denotes either a complex of necessities such as food, lodging, and laundry, and sometimes clothing or the amount needed to supply such a complex.
Support applies not only to the amount of money that provides maintenance but to the person who provides the means by which others are maintained.
Keep is a less dignified synonym of maintenance and is applicable not only to men but to animals.
Bread and bread and butter are synecdoches for living or sustenance, partly as a result of the use of the former in the Lord's Prayer "Give us this day our daily bread".