|Easton's Bible Dictionary|
A plant of the genus sinapis, a pod-bearing, shrub-like plant, growing wild, and also cultivated in gardens. The little round seeds were an emblem of any small insignificant object. It is not mentioned in the Old Testament; and in each of the three instances of its occurrence in the New Testament (Matthew 13:31, 32; Mark 4:31, 32; Luke 13:18, 19) it is spoken of only with reference to the smallness of its seed. The common mustard of Palestine is the Sinapis nigra. This garden herb sometimes grows to a considerable height, so as to be spoken of as "a tree" as compared with garden herbs.
Noah Webster's Dictionary
1. (n.) The name of several cruciferous plants of the genus Brassica (formerly Sinapis), as white mustard (B. alba), black mustard (B. Nigra), wild mustard or charlock (B. Sinapistrum).
2. (n.) A powder or a paste made from the seeds of black or white mustard, used as a condiment and a rubefacient. Taken internally it is stimulant and diuretic, and in large doses is emetic.
Int. Standard Bible Encyclopedia
mus'-tard (sinapi (Matthew 13:31 Mark 4:31 Luke 13:19 Matthew 17:20 Luke 17:6)): The minuteness of the seed is referred to in all these passages, while in the first three the large size of the herb growing from it is mentioned. In Matthew 13:32 it is described as "greater than the herbs, and becometh a tree" (compare Luke 13:19); in Mark 4:32 it "becometh greater than all the herbs, and putteth out great branches." Several varieties of mustard (Arabic, khardal) have notably small seed, and under favorable conditions grow in a few months into very tall herbs-10 to 12 ft. The rapid growth of an annual herb to such a height must always be a striking fact. Sinapis nigra, the black mustard, which is cultivated, Sinapis alba, or white mustard, and Sinapis arvensis, or the charlock (all of Natural Order Cruciferae), would, any one of them, suit the requirements of the parable; birds readily alight upon their branches to eat the seed (Matthew 13:32, etc.), not, be it noted, to build their nests, which is nowhere implied.
Among the rabbis a "grain of mustard" was a common expression for anything very minute, which explains our Lord's phrase, "faith as a grain of mustard seed" (Matthew 17:20 Luke 17:6).
The suggestion that the New Testament references may allude to a tall shrub Salvadora persica, which grows on the southern shores of the Dead Sea, rests solely upon the fact that this plant is sometimes called khardal by the Arabs, but it has no serious claim to be the sinapi of the Bible.
E. W. G. Masterman
Mustard (5 Occurrences)
Matthew 13:31 He set another parable before them, saying, "The Kingdom of Heaven is like a grain of mustard seed, which a man took, and sowed in his field; (WEB KJV WEY ASV BBE DBY WBS YLT NAS RSV NIV)
Matthew 17:20 He said to them, "Because of your unbelief. For most certainly I tell you, if you have faith as a grain of mustard seed, you will tell this mountain,'Move from here to there,' and it will move; and nothing will be impossible for you. (WEB KJV WEY ASV BBE DBY WBS YLT NAS RSV NIV)
Mark 4:31 It's like a grain of mustard seed, which, when it is sown in the earth, though it is less than all the seeds that are on the earth, (WEB KJV WEY ASV BBE DBY WBS YLT NAS RSV NIV)
Luke 13:19 It is like a grain of mustard seed, which a man took, and put in his own garden. It grew, and became a large tree, and the birds of the sky lodged in its branches." (WEB KJV WEY ASV BBE DBY WBS YLT NAS RSV NIV)
Luke 17:6 The Lord said, "If you had faith like a grain of mustard seed, you would tell this sycamore tree,'Be uprooted, and be planted in the sea,' and it would obey you. (WEB KJV WEY ASV BBE DBY WBS YLT NAS RSV NIV)