tertial

Etymology

From Latin tertius (“third”); the tertial feathers are the third row of feathers.

noun

1. (ornithology) Any flight feather attached to the humerus (upper arm) of a bird.
   He continues — "There was the same rear up, with the head bent down, followed by an upjerk of the hind parts; the long sickle-shaped tertials, so noticeable in this species, seemed little if at all expanded, […] 1923, Arthur Cleveland Bent, Life Histories of North American Birds: Wild Fowl, page 76