The etymology of this word may help people to remember it.
Deartháir comes from Old Irish derbráthair, from derb (“certain”) + bráthair (“brother”). The derbfine ("certain kin") was a kin group of four generations.
Here is a link that might be helpful for those wanting hearing the pronunciation of deartháir
(with thanks to galaxyrocker for the link)
The Duolingo exercises Mo dheartháir and Tá do dheartháir freagrach both have audio, though they contain the lenited dheartháir.
Makes me think of Flann O'Brien