甲乙丙丁 are the first four Heavenly Stems, used like A/B/C/D in Chinese. In contracts, 甲方 is 'Party A' and 乙方 is 'Party B.'
usage
甲 appears in many compounds: 指甲 (fingernail), 甲板 (deck of a ship), 装甲 (armored), 甲骨文 (oracle bone script).
Components
pictograph
甲jiǎ
shell; armor; first stem
Pictograph of a turtle shell or sprouting seed bursting through its husk - oracle-bone forms show a cracked rectangle with a tail dropping below. The same image powers all senses: armour, fingernail, and 'first' as in 甲乙丙丁. Indexed under Kangxi #102 田 by graphic resemblance, though 甲 isn't etymologically a field.
Filed under radical 田 (tián, #102) by convention. 田 is not a separate component in 甲, so no strokes are highlighted.
