ACH

ACH is a three-letter abbreviation with multiple meanings, as described below:

Acetylcholine (ACh), a neurotransmitter
Achondroplasia, a type of genetic disorder that is a common cause of dwarfism
Achnashellach railway station (United Kingdom), as the National Rail code for the station
Acholi language (ach), as the ISO 639 code for the language
Advanced Combat Helmet
Altenrhein Airport (Switzerland), as the IATA airport code
Automated Clearing House, a nationwide American electronic banking network
Air Changes per Hour, a measure of ventilation exchange rate in buildings