1) a service limited to a stated series of days
2) the class or course itself of priests who for a week at a time performed the duties of the priestly office. David divided the priests into twenty four classes, each of which in its turn discharged the duties of the office for an entire week, from sabbath to sabbath
Part of Speech: noun feminine
From G2184; diurnality, that is, (specifically) the quotidian rotation or class of the Jewish priests' service at the Temple, as distributed by families: - course.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root ἐφημερία; click on the second column to search for that grammatical form of the root ἐφημερία; click on the third column to search for that word and grammatical form; click on the total to search for the root ἐφημερία.