I’m particularly fond of “Jayus” and “Tartle”, and hope to be instrumental in introducing them into the American English lexicon. (From Maria Khordorkovksy)

Mamihlapinatapei
From Yagan, the indigenous language of the Tierra del Fuego region of South America. This word has been translated in several ways in English, always implying a wordless yet meaningful look shared by two people who both desire to initiate something but are both reluctant to start.

Jayus
From Indonesian, meaning a joke so poorly told and so unfunny that one cannot help but laugh.

Prozvonit
In both Czech and Slovak language, this word means to call a mobile phone only to have it ring once so that the other person would call back, allowing the caller not to spend money on minutes.

Kyoikumama
In Japanese, this word refers to a mother who relentlessly pushes her children toward academic achievement.

Tartle
A Scottish verb meaning to hesitate while introducing someone due to having forgotten his/her name.

Iktsuarpok
From the Inuit, meaning to go outside to check if anyone is coming.

Cafuné
From Brazilian Portuguese, meaning to tenderly run one’s fingers through someone’s hair.

Torschlusspanik
From German, this word literally means “gate-closing panic” and is used to describe the fear of diminishing opportunities as one ages. This word is most frequently applied to women who race the “biological clock” to wed and bear children.

Tingo
From the Pascuense language of Easter Island, it is the act of taking objects one desires from the house of a friend by gradually borrowing all of them.

Ilunga
From the Tshiluba language spoken in south-eastern Democratic Republic of the Congo, this word has been chosen by numerous translators as the world’s most untranslatable word. Ilunga indicates a person who is ready to forgive any abuse the first time it occurs, to tolerate it the second time, but to neither forgive nor tolerate a third offense.

 

Name any favorites or suggest other words to add to the list in comments.