1. 
   TH-fronting
   pronunciation of <th> as a <f> sound in words like thing or as a <v> sound in words like brother
   Found op http://www.bl.uk/learning/langlit/sounds/find-out-more/glossary/
   
   
2. 
   Th-fronting
   ``Th``-fronting refers to the pronunciation of the English "th" as "f" or "v". When th-fronting is applied, /θ/ becomes /f/ (for example, three is pronounced as free) and /ð/ becomes /v/ (for example, bathe is pronounced as bave). Th-fronting occurs (in many cases historically independently) in C...
   Found op http://en.wikipedia.org/wiki/Th-fronting
   
   

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