How to say "mechanism" in Japanese

• 機械きかいJLPT N3approx.Common
  nounPrimarily 'machine'; when it covers 'mechanism' the sense is a physical device or piece of apparatus, not an abstract process — for how a system works, メカニズム is the usual word.
  僕ぼくは今日きょうこの機械きかいを試験しけんするつもりです。↗

  I am going to put this machine to the test today.
• 過程かていJLPT N2approx.Common
  nounReally 'process' or 'course': the stages by which something unfolds. It matches 'mechanism' only in that process-like sense, so it is seldom the word you want for how a device or system works.
  その過程かていを彼かれに説明せつめいした。↗

  I explained the process to him.
• 機構きこうJLPT N1approx.Common
  nounThe mechanism or machinery of a device or system — how its parts are constructed and work together. Typical of technical and explanatory writing.
  どこか機構きこうが悪わるいに違ちがいない。↗

  Something must be wrong with the machinery.
• メカCommon
  nounA shortened form of メカニズム, also used for machines and mechanical equipment; for explaining how or why something happens, the full メカニズム is the usual choice.
• メカニズムCommon
  nounThe loanword is the usual choice for 'mechanism' in the abstract sense: how or why a phenomenon, system or process works, in scientific and everyday explanation alike.
  この機械きかいのメカニズムは複雑ふくざつです。↗

  The mechanism of this machine is complicated.

Choose 「メカニズム」 for how a phenomenon works, 機構 for mechanisms in technical prose, 機械 for physical machines, 過程 when you really mean process, and 「メカ」 as a short form of 「メカニズム」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 機械きかいmachine
• 過程かていprocess
• 機構きこうmechanism
• メカmechanism
• メカニズムmechanism
• 仕掛けしかけdevice
• 仕組みしくみstructure
• からくりmechanism
• 機序きじょmechanism
• 機械仕掛けきかいじかけmechanism
• 機械論きかいろんmechanism
• 機制きせいmechanism
• 機械装置きかいそうちmachine
• メカニックmechanism
• たねmechanism (of a magic trick, etc.)