Synecdoche
Etymology
From Greek synekdokhḗ, "a taking up together," from syn ("together") + ekdékhesthai ("to take, receive"). The idea is that one term is understood to take in more than it literally says. It has named this part-for-whole figure since ancient rhetoric and remains a specialized cousin of metonymy.
noun · /si-NEK-duh-kee/
Naming a whole by one of its parts, or a part by its whole.
What it names
The move behind "nice wheels" or "hired a hundred guns" — letting a vivid fragment carry the entire idea, which is why it feels more concrete than the full description.
Example
Calling the workforce "boots on the ground" is synecdoche — the footwear stands in for the soldiers wearing it.
Related idea
Metonymy substitutes an associated thing rather than a component; the boots in "boots on the ground" are part of the soldier, which makes it synecdoche specifically.