Definition of ESTRUS. : a regularly recurrent state of sexual excitability during which the female of most mammals will accept the male and is capable of conceiving: heat; also: a single occurrence of this state. See estrus defined for kids.
1. (medicine) any of various liquids sold as medicine (as by a travelling medicine show) but medically worthless. 2. communication (written or spoken) intended to deceive. Familiarity information: SNAKE OIL used as a noun is rare. Dictionary entry details.
In the keen Celtic mind, snake symbolic meaning of transformation came from the shedding of its skin. Physical evidence of leaving its form behind (casting off the old self), and emerging a sleeker, newer version made the snake a powerful symbol of rebirth and renewal.