almacantar /al-mə-kanˈtər/ or almucantar /al-mū-kanˈtər/ (astronomy)

1. A circle of altitude, parallel to the horizon
2. An instrument for determining a star's passage across an almacantar

• on purpose
• on record
• on remand
• on request
• onrush
• onrushes
• ons
• ONS
• on schedule
• on-screen
• on second thoughts
• onset
• onsets
• onsetter
• onsetters
• onsetting
• onsettings
• on shaky ground
• on shipboard
• on shore
• on-shore
• onshore
• onside
• onsides
• on sight