/əˌsētlˈkōˌlēn/ /ˌasitl-/
1. An organic, polyatomic cation that acts as a neurotransmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms including humans. (wikipedia.org)
2. Acetylcholine is one of many neurotransmitters in the autonomic nervous system (ANS) and is the only neurotransmitter used in the motor division of the somatic nervous system (sensory neurons use glutamate and various peptides at their synapses). Acetylcholine is also the principal neurotransmitter in all autonomic ganglia. (wikipedia.org)
3. (Biochemistry)
A neurotransmitter in humans and other animals. It is an ester of acetic acid and choline with chemical formula CH3COOCH2CH2N+(CH3)3. (wiktionary.com)
4. (Chemical, Neurology, physiology)
A chemical found in vertebrate neurons that carries information across the synaptic cleft, the space between two nerve cells. (biology-online.org)
5. A compound that occurs throughout the nervous system, in which it functions as a neurotransmitter. (Google dictionary)