甲乙
こうおつ first and second; A and B
Why it means this
甲 (first) + 乙 (second) — 'A and B'; the first two of the ten calendar stems, used like '1st, 2nd' or 'party A, party B'. 甲乙つけがたい, too close to rank.
Breakdown
Each character links to its full entry — origin story, stroke order, and readings.