Boyd’s Bible Dictionary:
(kol) (cap). A net for a woman’s hair (Isa. 3:18). In Hos. 13:8, the membrane around the heart.
Concise Bible Dictionary:
The diaphragm or midriff, which stretches above the liver all across the thorax (Ex. 29:13,22; Lev. 3:4,10,15; Lev. 4:9; Lev. 7:4; Lev. 8:16,25; Lev. 9:10,19). In Hosea 13:8 it is the pericardium, that which encloses the heart.
Strong’s Dictionary of Hebrew Words:
Meaning:
from 5462; properly, shut up, i.e. the breast (as inclosing the heart); also gold (as generally shut up safely)