youngest / most junior / tiny / one (unambiguous spoken form when spelling out numbers, esp. on telephone or in military) / one or ace on dice or dominoes / variant of 吆[yao1], to shout
二
=
一
:
Mnemonic symbol: a capacitor, because the two strokes remind me of the symbol in electrical drawings. Albert Einstein (Ø) is experimenting with a capacitor (二) in the space station's bathroom (Ø4). He finds that it's uncomfortable to discharge a capacitor using two flutes (一).