I. ˈtərshəl adjective
Etymology: Latin terti us third + English -al; from the fact that tertials form the third row of feathers
1. : of, relating to, or constituting the flight feathers borne on the basal joint of a bird's wing — compare primary 2c
2. : of, relating to, or constituting some of the innermost secondaries when different from the others or the scapular feathers — not used technically
II. noun
( -s )
: a tertial feather