Shadow-Casting Blade of a Sundial
Puzzle 17 of Animals with Weird Names Hard Pack
Question is: Shadow-Casting Blade of a Sundial
and the answer is: GNOMON
Word Meaning:
GNOMON — An object such as a pillar or a rod that is used to tell time by the shadow it casts when the sun shines on it, especially the pointer on a sundial.
Definitions from Wiktionary.