What is the word for pronouncing ‘th’ as ‘v’ as part of your English accent?

Some people I know have a ‘lazy tone’ on their British accent pronouncing their ‘th’ as ‘v’.

Don’t bover about the weava. (Don’t bother about the weather.)

It’s not a slur, because the ‘t’ in don’t and about is still there.

It’s not a lisp either.

My question is: What is the word for pronouncing ‘th’ as ‘v’ as part of your English accent?

Solution 1:

The linguistic feature is known as th-fronting, where a dental fricative (both th-sounds) becomes a labiodental fricative (f,v) while the voicing remains the same. First noted in the late 18th c., it is now a common feature of several dialects of English: Cockney, Essex dialect, Estuary English, some West Country and Yorkshire dialects, Newfoundland English, and African American Vernacular English. Most recently, it’s been attested in, of all places, Glasgow.

The feature is used to comic effect in Catherine Tate’s character Lauren Cooper and her catchphrase “Am I bovvered?” which during Comic Relief 2007 then-PM Tony Blair unleashed on Lauren instead. Blair doesn’t quite manage the pronunciation.

You can even buy the t-shirt:

Solution 2:

This is called

th-fronting

A 'th' (voiced or not) is a dental fricative (the tip of the tongue behind the top front teeth). Fronting it (moving articulation more forward) is to the labiodental position, the lower lip contacting the front upper teeth.

'Th' is a rare sound in the world's languages (some varieties of Spanish (Castilian) and Arabic (MSA), are notable for having it). It is easy for it to be articulated by language learners as some nearby thing instead, as a stop (t/d) or alveolar (s/z), at the ridge behind the top front teeth), in addition to fronting.

Th-fronting is a feature of some speakers of Cockney/Estuary English and African-American English (AAE) and related varieties of Southern American English. I say 'some speakers' because it is not a feature for all speakers of these varieties like r-dropping might be)