吼 means something along the lines of **cry** or **roar**.  So think of it as a noise like 鳴.

 - 吼(ほ)える = to bark, to bellow, to howl, to cry
 - 咆吼 (ほうこう) = a howl, cry (alternative to 咆哮)
 - 獅子吼 (ししく) = lion’s roar
- 帆猿 ( ほえざる) = Howler Monkey
- 吼え声 (ほえこえ) = a bark, a howl

So I guess it’s a term that’s made up in an anime or game. You said it was used in a song? It sometimes happens they coin new words in those (especially in anime and game related music). For the pronunciation you’d have to listen to the song though. If I had to make a guess, it would be **てんこう**. 

The meaning, however, is straightforward: **heavenly roar**.

edited: provided more examples.