送 means 'to deliver/send' and 死 means 'death' — you're literally delivering yourself to death. The image of walking up and handing yourself over to death makes it memorable.
usage
送死 is almost always used in warnings or emotional outbursts. The pattern 去送死 (go court death) is especially common. Compare with 找死 (zhǎosǐ, asking for it) which implies recklessness rather than hopelessness.
