tranquilize

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.

1. To become tranquil; relax.
2. To have a calming or soothing effect.

verb

To make or become calm: allay, balm, becalm, calm (down), lull, quiet, settle, still. See calm/agitation.

Definition: make calm, quiet
Antonyms: aggravate, agitate, incite, stir up, upset

1. To make tranquil; pacify.
2. To sedate or relieve of anxiety or tension by the administration of a drug.
3. To become tranquil; relax.
4. To have a calming or soothing effect.

The verb has 2 meanings:

Meaning #1: make calm or still
  Synonyms: calm, calm down, quiet, tranquillize, tranquillise, quieten, lull, still

Meaning #2: cause to be calm or quiet as by administering a sedative to
  Synonyms: sedate, calm, tranquillize, tranquillise