5th calendar sign
戊 is the fifth of the ten calendar signs in the traditional Chinese sexagenary cycle. Its meaning is purely calendrical, with no concrete object or action associated.
戊 originated as a pictograph of a pole weapon, but its modern use is purely as a calendrical sign. The historical connection between the weapon image and the calendar sign is uncertain.
Picture a pole weapon standing upright like a marker in a calendar grid, representing the fifth position.
For ボ, imagine a bow (as in bow and arrow) shaped like the character 戊, marking the fifth sign: bow -> ボ.
Boshin War (Japanese civil war between Imperial and shogunate forces; 1868-1869)
5th in rank; fifth sign of the Chinese calendar
Earth Horse (55th term of the sexagenary cycle, e.g. 1918, 1978, 2038)
fifth division of the night (approx. 3am to 5am)
Earth Rat (25th term of the sexagenary cycle, e.g. 1948, 2008, 2068)
Earth Tiger (15th term of the sexagenary cycle, e.g. 1938, 1998, 2058)
Earth Dog (35th term of the sexagenary cycle, e.g. 1958, 2018, 2078)
Earth Monkey (45th term of the sexagenary cycle, e.g. 1908, 1968, 2028)
Imperial Rescript of 1908
person whose physical suitability for conscription in the former Japanese military could not be determined in that year (e.g. due to illness)
Earth Dragon (5th term of the sexagenary cycle, e.g. 1928, 1988, 2048)