Mamihlapinatapai,

The word Mamihlapinatapai is derived 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 allegedly refers to "a look shared by two people, each wishing that the other would initiate something that they both desire but which neither wants to begin."