ガツ, ガチ, タイ, がつへん, いちたへん, しにがまえ
bare bone, bad, wrong, death radical (n. 78)
JLPT0 G13 S0 F5000
The relevant seal inscription form is a variant of 冎 (bone circulating in its joint) + a line# indicating severance → *severed bone* → *bone*; *death* (resulting from the body being severed). Also, *bad/wicked* (← wicked deed).
[Full Kanji Etymology List]