Labor, or labour if one favors the Anglo spelling: productive work, especially physical toil done for wages; or those who perform such work. Also, the process of childbirth; and related, at least metaphorically, something done for pleasure rather than gain (as in a labor of love).
Few words run such a gamut of meanings and are yet so intimately tied to our everyday lives. Most of us labor for a living, yet few do so manually in this day and age because such activities are more often done more cheaply, and efficiently, by machines. Labor itself has changed. Our labor is often not of muscle but of intellect: 'knowledge workers' is a modern contrivance communicating this shift. Whether it is in the ephemeral transactions of customer service, the abstractions of finance and law, or the crafting of the written word, we labor as hard as previous generations ever did - if only in mind, rather than in body.
For writers this is especially true - many of us labor to bring ideas themselves into existence, partaking of both the 'childbirth' and 'labor of love' aspects of the word. We write to give birth to the fruits of our imaginations, and we love what we do despite the effort and dedication and patience it requires. No few of us would be far happier to dig a ditch or split logs for a few hours rather than go through another editing session! But of such timber are our word-temples built, and with such sweat do our words coalesce from the aether of imagination to appear, solid and substantial, from the amorphous mists of the creative process. And if anyone tells you this is not a labor - of love or otherwise - they may safely be called a stinkin' liar.