diaeresis or dieresis /dī-ērˈi-sis or -erˈ/

1. A mark ( ¨ ) placed over a vowel, esp the second of two adjacent ones to show that it is to be pronounced separately, as in naïf
2. A pause or break where the end of the word coincides with the end of a foot (prosody)

• testis
• test-market
• test-marketed
• test-marketing
• test-markets
• test match
• test matches
• teston
• testons
• testoon
• testoons
• testosterone
• testosterones
• test paper
• test papers
• test pattern
• test patterns
• test pilot
• test pilots
• testril
• testrill
• testrills
• testrils
• tests
• test the water