The word 'tach' is a modern English abbreviation, a back-formation from the longer technical terms 'tachometer' or 'tachograph'. These source words themselves derive from Greek: 'tachos' (speed, swiftness) combined with '-meter' (measure) or '-graph' (writing instrument). The clipping process follows a common pattern in technical jargon, where a familiar initial syllable is retained to create a concise, informal term used primarily in professional or enthusiast contexts, such as automotive or aviation fields.

This word is a simplex, a clipped form of longer technical terms. It is not productively formed from independent morphemes in its current spelling.