Comment by astrobe_

Maybe OP refers to vocabulary search order manipulation [1]. It's sort of like namespaces, but "stacked". There's also the old MARKER and FORGET pair [2].

The dictionary pointer can also be manipulated in some dialects. That can be used directly as the stack variant of the arena allocator idea. It is particularly useful for text concatenation.

[1] https://forth-standard.org/standard/search [2] https://forth-standard.org/standard/core/MARKER