means A butterfly-shaped gland in your neck that releases hormones controlling how fast your body burns energy.

from From Greek 'thyreoeides,' meaning 'shield-shaped' — from 'thyreos,' an oblong, door-shaped shield (itself from 'thyra,' a door). The early anatomists weren't naming the gland but the nearby cartilage it sat behind, which reminded them of that big shield; the name later migrated onto the gland itself.