dialect: [16] The notion underlying dialect and its relatives dialectic [14] and dialogue [13] is of ‘conversation’. They come ultimately from Greek dialégesthai ‘converse’, a compound verb formed from the prefix dia- ‘with each other’ and légein ‘speak’ (source of English lecture and a wide range of related words). This formed the basis of two derived nouns.
First diálektos ‘conversation, discourse’, hence ‘way of speaking’ and eventually ‘local speech’, which passed into English via Latin dialectus and Old French dialecte (from it was produced the adjective dialektikós ‘of conversation, discussion, or debate’, which was eventually to become English dialectic). Secondly diálogos ‘conversation’, which again reached English via Latin and Old French. => lecture
dialect (n.)
1570s, "form of speech of a region or group," from Middle French dialecte, from Latin dialectus "local language, way of speaking, conversation," from Greek dialektos "talk, conversation, speech;" also "the language of a country, dialect," from dialegesthai "converse with each other," from dia- "across, between" (see dia-) + legein "speak" (see lecture (n.)).