The word carat comes from the Carob Mediterranean tree whose seed was used for centuries as the standard of weighing precious gems. Each carob seed weighs approximately one-fifth of a gram. A carat is one-fifth of a gram.
Jewelry & Diamond Industry Dictionary of Terminology
Horology is the scientific study of time. Specifically, horology involves the measurement of time and the art of making instruments for indicating time.
Sources for these definitions are GIA.edu, Google.com, Meriam-Webster.com, and Wikipedia.org.