an area with sides higher than the center: an indentation, a depression, a dip, a divot, a hole / (slang) female genitalia, the vagina

burr (on an edge)

三五: fifteen; three and five; alternate for 琵琶 (biwa, “a traditional biwa lute”) / 参伍: mixing together, mixture / 珊瑚: coral / 産後: after childbirth, the postpartum period

数字: numbers / 数次: number of times