aboard: 在船(或飞机，车)上。如：I never went aboard a ship.
broad: 为形容词，宽广的。如：He has very broad shoulders.
abroad: 副词，在国外或海外。如：He often goes abroad.
board: 为动词，上(船，飞机，车)。如：The passengers are boarding the plane now.
be to do: 侧重意志,计划,安排I'm to meet him.(含双方事先约好的意思)
be going to: 侧重打算,想法
be about to: 表最近的将来,后面不接时间状语