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HDOHigh Definition Optics (various companies)
HDOHealth Delivery Organization (various organizations)
HDOHigh Density Overlay (phenolic resin-impregnated plywood used in concrete forms)
HDOHuman Development Organization (Sri Lanka)
HDOHoly Day of Obligation
HDOHearing Designation Order (FCC proceedings)
HDOHealthcare Discount Organization (Addvantage Care)
HDOHeavy Duty Oil
HDOHigh Demand Occupation
HDOHumanitarian Demining Operation
HDOHydrogen Deuterium Oxide
HDOHeadache During Orgasm
HDOHomeland Defense Office
HDOHousing Development Office
References in periodicals archive ?
A solemn Catholic holy day of obligation commemorating the Holy Eucharist.
In 1708, Pope Clement XI declared December 8 as a holy day of obligation for Catholics al over the world in honor of holiness and purity of the Blessed Virgin Mary.
While not a holy day of obligation, this was a day when churches are packed with devotees as well as those lining up for the imposition of the ash.
Alma de Cuba, Seel Street Christmas is a Holy Day of Obligation, so give a nod to Him upstairs by calling into this former church on your pilgrimage through town.
You had to prepare to fast because the next day was Ash Wednesday, a holy day of obligation.