tran·quil·iz·er also tran·quil·liz·er 
(trăngkwə-līz′ər, trăn-)
(trăngkwə-līz′ər, trăn-)n.
1. One that serves to tranquilize, as soothing music.
2. Any of various drugs used to reduce tension or anxiety; an antianxiety agent.
3. Any of various drugs used to treat psychotic states; an antipsychotic drug. Not in scientific use.