Learn how to say Celsius correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word Celsius:
[postpositive when used with a numeral]
of or denoting a scale of temperature on which water freezes at 0° and boils at 100° under standard conditions:
a temperature of less than 25° Celsius
(also Celsius scale) the Celsius scale of temperature.
Celsius rather than centigrade is the standard accepted term when giving temperatures: use 25° Celsius rather