Abarim Publications' online Biblical Greek Dictionary
The particle δε (de) indicates a mild objection or simple transition and can sometimes be translated with "but" or "indeed, but" or "also". More often, however, it carries the mere force of a sentence's natural progression and as a result leaves little to be translated in English. Hebrew has a silent particle like that as well, albeit of slightly different function and origin: את ('et).
Our particle δε (de) frequently occurs with other particles in formulaic contexts: with μεν (men), which expresses affirmation, it forms a construct that means something like "indeed" or "if truly... then surely" (see our article on μεν, men, for an exhaustive look at this formula). With the copulative και (kai) it literally forms "and but" but takes on the meaning of "also".
Our particle δε (de) is used 2867 times in the New Testament; see full concordance.
The obviously related adverb δη (de) serves as a particle of confirmation or affirmation: truly, by all means. It is used 6 times, see full concordance, and from it derive: