Thornback var addthis_config = {"data_track_addressbar":true};

Thornback is a Tyranid Biomorph.

In 4th Edition Thronback is a nickname given by Imperial Guard soldiers to Tyranids with large blade protrusions from their carapace. They are often seen charging into ranks of soldiers using pure body mass as their primary weapon and simply impaling any enemies it comes across.^1-p33

Sources

• ¹:Codex: Tyranids (4th Edition) (identical entry in Warhammer 40,000: Wargear p62)