Etymology of Threnodite system

[CCQ]

I recently found out that Threnody means a lament, Elegy (another planet in the system) is a sad poem, usually written to praise and express sorrow for someone who is dead and Monody is a poem lament also. These are three of the four systems in Threnodite the fourth being Purity. 

1) Why is that planet called Purity? 

2) Why are those three all sad and death words?

I thought that maybe it is because the fight between Odium and Ambition took place on those 3 planets but not the 4th. Or for whatever reason Silence considers her world cursed is also on the other 2. Any thoughts on the system?

[HoidistheStick]

Also, the moon of Elegy is named Coronach, which, according to Wikipedia, is a Scottish type of lamentation for the dead, sung at funerals.  

[Hemalurgic Headshot]

I bet something special is going on with Purity, but of course, since we know very little about Therondy, we might not know for a while.

[Farnsworth]

Ambition died on Threnody, so the planets are all laments to Ambition. As for purity, I think it may be a shard. It is bigger than the sun after all.

[Yata]

7 hours ago, Figberts said:

Ambition died on Threnody, so the planets are all laments to Ambition. As for purity, I think it may be a shard. It is bigger than the sun after all.

Ambition didn't die there. Simply part of his fight with Odium happened there