rosh hodesh

from The Century Dictionary.

• noun The first day of the Jewish month which begins with the new moon. On the first day (some times two days) of the month the ritual is distinguished by additional prayers including hallel (which see). See also Jewish festivals.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (Judaism) the beginning of each month in the Jewish calendar; marked by a special liturgy