I've been rereading Heinlein's "Notebooks of Lazarus Long" recently and came across this phrase:
People who go broke in a big way never miss any meals. It is the poor jerk who is shy half a slug who must tighten his belt.
I understand what "shy (of)" means but I've checked dictionaries and can't figure out what "slug" refers to here. They propose meanings similar to this list:
bullet or a cylindrical piece of metal
shot of an alcoholic drink
I don't really see any of them fitting here. From the way it's said it seems to mean something (not very) valuable since the "poor jerk" is not "broke in a big way" but still has to "tighten his belt" = go without a meal or two.
IIRC the original books date from 1950s-60s.
The original book (Time enough for love) was written in the early 1970s.