Mamihlapinatapai (sometimes spelled mamihlapinatapei) is a word from the Yaghan language of Tierra del Fuego, listed in The Guinness Book of World Records as the "most succinct word", and is considered one of the hardest words to translate. 

It refers to "a look shared by two people, each wishing that the other will offer something that they both desire but are unwilling to suggest or offer themselves."