voracious, gluttonous
餮 centers on excessive, greedy consumption: being voracious or gluttonous, devouring food without restraint.
餮 combines 食 (food/eat) with 殄, which likely contributes the sound and carries a sense of exhaustion or ending, together suggesting consuming everything greedily.
The top part 殄 looks like something being destroyed or exhausted, and the bottom is 食 (food). Imagine a glutton devouring food until nothing is left, a voracious eater who exhausts every dish.
For テツ, picture a glutton at a table eating so much that the table legs bend like tetanus-stiff metal: tets -> テツ, and the greedy eater keeps going.