means The act of combining separate elements, ideas, or substances into a unified, coherent whole.

from From Greek synthesis, "a putting together," built from syn- "together" and thesis "a placing" (from the root tithenai, "to put"). That same thesis underlies words like hypothesis and antithesis — a whole family of placings. The word arrived in English by the 1600s, first in the language of logic and philosophy, and later flooded into chemistry, where it still names the patient art of building one compound out of many.