tertialOf the third rank or row among the flight-feathers of a bird's wing; tertiary, as a quill-feather.
ntertialA tertiary flight-feather; one of the pennæ, or large feathers, of a bird's wing of the third set, which grow on the elbow or upper arm; one of the tertiaries. The word was intended to signify only the third set of flight-feathers, in the same relation to the humerus that the secondaries bear to the ulna, and the primaries to the manus; but in practice two or three of the innermost secondaries are called tertials when in any way distinguished from the rest. Also tertiary, tertiary feather. See cuts under bird and covert, n., 6.
Chambers's Twentieth Century Dictionary
adjTertialter′shal of the third rank among the flight-feathers of a bird's wing
nTertiala tertiary flight-feather
Webster's Revised Unabridged Dictionary
From L. tertius, third, the tertial feathers being feathers of the third row. See Tierce