tertiary , adj :
Of third rank or order; subsequent. (chemistry) Possessing some quality in the third degree; especially having been subjected to the substitution of three atoms or radicals. (ornithology) Of quills: growing on the innermost joint of a bird’s wing; tertial.
Source http://handbookblogger.blogspot.com/2017/07/tertiary-word-of-day-for-july-29-2017.html
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