Systematic is the more common word; it most often describes something that is done according to a system or method. Systemic describes what relates to or affects an entire system, be that system …

SYSTEMATIC definition: having, showing, or involving a system, method, or plan. See examples of systematic used in a sentence.

Planning, expecting and arranging systematically (Definition of systematic from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

Definition of systematic adjective from the Oxford Advanced Learner's Dictionary. done according to a system or plan, in a complete, efficient or determined way. The prisoner was subjected to systematic …

1. Characterized by, based on, or constituting a system: systematic thought. 2. Working or done in a step-by-step manner; methodical: a systematic worker; a systematic approach.

There are 11 meanings listed in OED's entry for the word systematic, four of which are labelled obsolete. See ‘Meaning & use’ for definitions, usage, and quotation evidence.

Biology concerned with classification: systematic botany. Biology pertaining to, based on, or in accordance with a system of classification: the systematic names of plants.

systematic meaning, definition, what is systematic: organized carefully and done thoroughly: Learn more.

Something that is done in a systematic way is done according to a fixed plan, in a thorough and efficient way. They began a systematic search.

She made a systematic study of the evidence. He is very systematic [= methodical] in his work. We approached the problem systematically.