Marginal definition, pertaining to a margin. Even those who did fight against the Russians played only a marginal role in determining the outcome of the war. Marginal man · Marginal note · Marginal cost. Define marginally (adverb) and get synonyms. What is marginally (adverb)? marginally (adverb) meaning, pronunciation and more by Macmillan Dictionary. Marginally definition, pertaining to a margin. Did Chuck Hagel Cave? That means that if the lease is up on a store which is only marginally profitable, you.