01 A day which is a term (as for payment of rent), or is a day in a term, as of the sitting of a court; esp., one of a series of special days,…
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1.
A day which is a term (as for payment of rent), or is a day in a term, as of the sitting of a court; esp., one of a series of special days, designated by scientists of different nations or stations, for making synoptic magnetic, meteorological, or other physical observations.