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Wiktionary
microarchitecture

n. 1 (context biology English) The detailed structure of any organ etc. at a very small scale 2 (context computing English) The architecture of the data processing parts of a microcomputer

Wikipedia
Microarchitecture

In electronics engineering and computer engineering, microarchitecture, also called computer organization and sometimes abbreviated as Āµarch or uarch, is the way a given instruction set architecture (ISA) is implemented in a particular processor. A given ISA may be implemented with different microarchitectures; implementations may vary due to different goals of a given design or due to shifts in technology.

Computer architecture is the combination of microarchitecture and instruction set designs.