1. to extremes; - Example: "he went overboard to please his in-laws"
2. from on board a vessel into the water; - Example: "they dropped their garbage overboard"
The Collaborative International Dictionary of English v.0.48:
Overboard \O"ver*board`\, adv.
Over the side of a ship; hence, from on board of a ship, into
the water; as, to fall overboard.
To throw overboard, to discard; to abandon, as a dependent
To go overboard, to go to an extreme; to overdo; as, he
went overboard at the buffet and got an upset stomach.
[1913 Webster +PJC]
WordNet (r) 3.0 (2006):
adv 1: to extremes; "he went overboard to please his in-laws"
2: from on board a vessel into the water; "they dropped their