IPA: /pərˈtɪnənsi/
KK: /pɜrˈtɪnənsi/
The quality of being relevant or related to the topic being discussed.
The pertinency of her comments made the discussion more meaningful.
Pertinency is formed from "pertinens" (meaning pertaining or relating) and the suffix "-cy" (meaning the state or quality of). The word refers to the quality of being relevant or applicable to a matter.
Think of something that is 'pertaining' to a topic — that's why 'pertinency' means the quality of being relevant.