Concise Bible Dictionary:
The word elam occurs only in Ezekiel 40:21-36, and in the AV (KJV) is translated “arch”; but this is judged not to be its meaning, though it is not at all certain as to what it really refers. In the margin it reads, “galleries” or “porches,” elsewhere “vestibule,” and again “projection.”
Strong’s Dictionary of Hebrew Words:
Meaning:
or (shortened) ;elam {ay-lawm'}; or (feminine) ielammah {ay-lam-maw'}; probably from 352; a pillar-space (or colonnade), i.e. a pale (or portico)