IPA: /ˈtɔːlnəs/
KK: /tɔlnəs/
The quality or state of being of a greater than average height.
Her tallness made her stand out in the crowd.
Tallness → It is formed from "tall" (of uncertain origin, possibly from Middle English *tal*, meaning high or lofty) and "-ness" (meaning the state or quality of). The word "tallness" refers to the state of being tall or the quality of height.
Think of the word 'tall' to remember that 'tallness' means the quality of being tall.