tran·quil·ize also tran·quil·lize 
(trăngkwə-līz′, trăn-)
(trăngkwə-līz′, trăn-)v. tran·quil·ized, tran·quil·iz·ing, tran·quil·iz·es also tran·quil·lized or tran·quil·liz·ing or tran·quil·liz·es
v.tr.
1. To make tranquil; pacify: "Nothing contributes so much to tranquilize the mind as a steady purpose" (Mary Shelley).
2. To sedate or relieve of anxiety or tension by the administration of a drug.
v.intr.
1. To become tranquil; relax.
2. To have a calming or soothing effect.
tran′quil·i·zation (-kwə-lĭ-zāshən) n.