a regular, full-time job, esp. as distinct from some other pursuit that is less remunerative and more uncertain
from the usual hours of such a job
See day job in American Heritage Dictionary 4
One's primary job, usually at daytime and enabling one to pursue a secondary activity from which one would eventually like to draw an income: “She took a day job as a bank teller in Lubbock; nights, she played in pickup games, but she didn't have a trainer, a coach, or a team”(Elizabeth Royte).