IPA: /ˈʌndərˌbɪdə/
KK: /ˈʌndərˌbɪdər/
A person who places a bid in an auction that is lower than another bid, often being the second-highest bidder.
In the auction, the underbidder was disappointed when the winning bid exceeded his offer.
Underbidder → It is formed from "under-" (meaning below or beneath) and "bidder" (from the verb "bid", meaning to offer a price). The word refers to a person who offers a price that is lower than others in a bidding situation.
Think of someone who offers a price that is 'below' ('under-') what others are offering — that's why an underbidder is someone who bids lower.