コウ, ゴ, きさき
empress, queen, after, behind, back, later
JLPT1 G6 S6 F1583
The relevant seal inscription form is the reverse of the elements combined in 司 (peer through a narrow hole), and thus refers to someone kept out of sight → *empress*; *queen* (← female members of the royal/imperial family, whose quarters were secreted deep within a palace; compare 宮).
[Full Kanji Etymology List]