Mat 13:31 Another parable put he forth unto them, saying, The kingdom of heaven is like to a grain of mustard seed, which a man took, and sowed in his field:
Luke 13:18 Then said he, Unto what is the kingdom of God like? and whereunto shall I resemble it?
Luke 13:19 It is like a grain of mustard seed, which a man took, and cast into his garden; and it grew, and waxed a great tree; and the fowls of the air lodged in the branches of it.
Here we see both terms used interchangeably in the parable of the mustard seed.