NEHELAMITE (nē-hĕl'a-mīt, Heb. hanĕ- helāmî). Shemaiah, a false prophet, an adversary of Jeremiah, is styled a Nehelamite (Jer.29.24, Jer.29.31-Jer.29.32). The place-name Nehelam is not found in the OT.

NEHELAMITE nĭ hĕl’ əm īt (הַנֶּחֱלָמִ֖י, dweller of Nehelam). An epithet applied to Shemaiah, one of the false prophets who opposed Jeremiah and whom he rebuked (Jer 29:24, 31, 32 KJV, ASV). The RSV has “of Nehelam,” but no such place name is found in the OT. It could be a family name. The KJVmg. has “dreamer,” apparently because the etymology suggests a connection with the Heb. חָלַם, H2731, “to dream.”

International Standard Bible Encyclopedia (1915)

ne-hel’-a-mit, (ha-necheldmi): The designation of Shemaiah, a false prophet who opposed Jeremiah (Jer 29:24,31,32). The word means "dweller of Nehelam," but no such place-name is found in the Old Testament. Its etymology, however, suggests a connection with the Hebrew chalam, "to dream," and this has given rise to the rendering of the King James Version margin "dreamer."