Tinder is suing the 'Tinder for threesomes' app

Tinder is going to war against an alternative dating app that many refer to as the "Tinder for threesomes."

The wildly popular Match Group-owned dating app is suing 3nder, a far smaller British dating app aimed at polyamorous individuals and those with alternative sexualities. Although it is not marketed as such, it is often referred to as "Tinder for threesomes."

Tinder alleges that 3nder's name - superficially similar to Tinder - infringes on its trademark. It wants its smaller rival to completely close down and stop using the 3nder name. Romanian 3nder founder Dimo Trifonov says he intends to fight.

Tinder first filed a cease-and-desist against 3nder in December 2015, to which Trifonov declined to agree. After several months of nothing, Tinder's lawyers hit Trifonov with a response on May 10, saying they plan to begin proceedings for trademark infringement.

In his original response, Trifonov flatly denies that 3nder's name is derived from Tinder's. "The name reflects the original concept that I developed involving the contraction of the world 'three' and 'friender' and my choice of word had nothing to do with the Tinder word used by your clients," the CEO wrote. "Phonetically the most obvious and intended pronunciation of the brand is therefore 'Three-ender' not 'Thrinder' as you suggest, which makes neither phonetic sense, nor bears any relation to the underlying app itself."

A press release from 3nder also points out that other dating brands besides Tinder - including Grindr and Adult Friend Finder - use a "nd(e)r" suffix.

3nder, which has raised $500,000 in funding and claims to have 3 million messages sent on its platform every month, is obviously keen to frame this as a David-versus-Goliath style battle between a perky startup and a huge incumbent.

In a statement, Trifonov said: "3nder believes in a world where innovation, freedom of expression and the rights of small businesses are in the economic and social interests of society. There is a robust history of large companies attacking small businesses. 3nder acknowledges the impact Tinder has had on the world by introducing 'swipe dating' but harbours zero ambitions to be similar. We target an audience with completely different needs."

Tinder did not immediately respond to a request for comment.

3nder is iOS only, with an Android release due soon.