Eclectic
Eclectic describes a design that deliberately draws on multiple styles, periods or sources, combined so the result reads as coherent rather than accidental.
Eclecticism is a considered strategy, not an absence of one. It works when a unifying thread holds the mix together, usually a consistent palette, a repeated material, or a disciplined approach to proportion.
It appears frequently in renovation work, where a period cottage or terrace gains a contemporary addition. The old and new are not pretending to be each other; the contrast is the point, and the connection between them is what has to be designed carefully.
The failure mode is incoherence, where too many references compete and none dominates. The usual discipline is to let one language lead and treat the others as accents.