noun
arc of recess (gear)
A technical term in gear design referring to the portion of the pitch circle where a pair of gear teeth are disengaging after contact.
歯車の設計では、遠退き弧の長さが騒音に影響する。
In gear design, the length of the arc of recess affects noise.
Compound of 遠退き (とおのき, 'receding, moving away') and 弧 (こ, 'arc'). The exact historical derivation is uncertain; the term is a technical coinage for gear geometry.