The German, Swedish, Danish and Norwegian word gift means "poison". What's up with that?
Proto-Germanic *ǥiftiz meant "something given or received", and that meaning is found in German Mitgift "dowry", and Dutch gift (altho the Dutch word can also mean "poison"). Something went horribly wrong semantically, and according to Grimm it happened in the 19th century, which is when the "poison" meaning arose in German. Then in the last third of the 19th century, the "poison" meaning was borrowed from German into Swedish, Danish, and Norwegian.
Old Norse gipt is "something given or received" - this is the source of the /g/ of modern English gift. Old English ȝift meant "payment for a wife", but we know it was replaced or influenced by the Old Norse word, because otherwise the modern word would be yift.
*ǥiftiz is from Proto-Indo-European *gʰebʰ-ti- from *gʰebʰ- "to give or receive". In Latin, the form *gʰabʰ-eh₂- (*-eh₂- formed stative denominative verbs) became habeō "to hold, possess" and habitus "condition, state, habit" (why did *bʰ not become f?) [answer: because it's not word-initial, thanks _duif]. Latin male habitus "in poor condition" became Old French malade "sick". The phonological development was something like male habitum - malabitum - malabde - malade. This was borrowed into English and became malady.
The image is one of Tove Jansson's illustrations for Moominpappa's Memoirs (Muminpappans memoarer).