A — 1: διαθήκη
(Strong's #1242 — Noun Feminine — diatheke — dee-ath-ay'-kay )

primarily signifies "a disposition of property by will or otherwise." In its use in the Sept., it is the rendering of a Hebrew word meaning a "covenant" or agreement (from a verb signifying "to cut or divide," in allusion to a sacrificial custom in connection with "covenant-making," e.g., Genesis 15:10 , "divided" Jeremiah 34:18,19 ). In contradistinction to the English word "covenant" (lit., "a coming together"), which signifies a mutual undertaking between two parties or more, each binding himself to fulfill obligations, it does not in itself contain the idea of joint obligation, it mostly signifies an obligation undertaken by a single person. For instance, in Galatians 3:17 it is used as an alternative to a "promise" (vv. 16-18). God enjoined upon Abraham the rite of circumcision, but His promise to Abraham, here called a "covenant," was not conditional upon the observance of circumcision, though a penalty attached to its nonobservance.

Galatians 3:15Luke 1:72Acts 3:25Romans 9:411:27Galatians 3:17Ephesians 2:12Hebrews 7:228:6,8,1010:16Deuteronomy 2930 Hebrews 7:18Hebrews 7:22Hebrews 8:99:20Acts 7:82—Corinthians 3:14Hebrews 9:4Revelation 11:19Matthew 26:28Mark 14:24Luke 22:201—Corinthians 11:252—Corinthians 3:6Hebrews 10:2912:2413:20Hebrews 9:15Hebrews 8:7Hebrews 7:22Hebrews 9:16,17TESTAMENT.
B — 1: συντίθημι
(Strong's #4934 — Verb — suntithemi — soon-tith'-em-ahee )

lit., "to put together," is used only in the Middle Voice in the NT, and, means "to determine, agree," John 9:22; Acts 23:20; "to assent," Acts 24:9; "to covenant," Luke 22:5 . See AGREE , ASSENT.

Matthew 26:15