1830, from synthesis + -ize. A correct formation would be *synthetize. Related: Synthesized; synthesizing.
synthesize syn·the·size (sĭn'thĭ-sīz')v. syn·the·sized, syn·the·siz·ing, syn·the·siz·es
To combine so as to form a new, complex product.
To form or produce by chemical synthesis.