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.
这组词都有“口头表达的”的意思,其区别是:
oral: 侧重指用嘴进行表达或交流。
verbal: 指口头进行,但不排除使用文字的可能性。