Comprehensive resource for understanding and mastering English idioms
The idiom "on board" means to be a part of something, usually a group or project, and to support it wholeheartedly. It can also refer to being physically present in a particular location or situation.
The idiom "on board" dates back to the 16th century. It originally referred to being physically present in a ship or boat, either as a passenger or crew member. Over time, it evolved to refer more broadly to being involved or committed to something, whether that be a project or cause. There are no significant regional variations of this idiom.