Borlad

The Etymologies in volume V of The History of Middle-earth give special attention to the names of Bór and his sons, and from that source we can be sure that the Bor- element of Borlad's name means 'faithful'. That is, he was one of those who remained faithful to the cause of the Elves (which implies that he was given the name after the events of the Nirnaeth, in which he demonstrated this faithfulness).

Unfortunately the names of Bór's sons addressed in The Etymologies belong to an earlier phase of Tolkien's writing, and are not quite the same as those in the published Silmarillion. The Etymologies name the sons as Borthandos, Borlas and Boromir, but by the time of the Silmarillion texts these had become Borlad, Borlach and Borthand. Thus we are lacking an explanation of the -lad element of Borlad's name. (Lad is indeed a well-attested Elvish word, meaning 'open land, plain', but that meaning does not seem to apply in Borlad's case, so we must assume that the element comes from some other source.)