蟻の門渡り

Noun

 * 1) perineum
 * 2) a narrow pass, a precipice
 * 1) a narrow pass, a precipice

Usage notes
Literally “ants’ passage”, the phrase appears in nature poetry from the 12th century referring to lines of ants walking on the ground. The popular sense “perineum” alludes to an 18th century work by about lice crossing the “valley of the underwear”.