early 14c., "confute or frustrate an opponent in argument, end an argument by winning it," from Latin concludere "to shut up, enclose," from assimilated form of com "together" (see con-) + -cludere, combining form of claudere "to shut" (see close (v.)).
Meanings "reach a mental determination, deduce; infer or determine by reason" are from late 14c., a sense also in Latin. General sense of "bring to an end, finish, terminate," and intransitive sense of "come to an end" are from late 14c. Meaning "settle, arrange, determine finally" is from early 15c. Sometimes in Middle English it was used in the etymological sense, "shut in" (late 14c.). Related: Concluded; concluding.