'Sea level' definitions:
Definition of 'sea level'
(from WordNet)
noun
Level of the ocean's surface (especially that halfway between mean high and low tide); used as a standard in reckoning land elevation or sea depth
Definition of 'Sea level'
From: GCIDE
- Sea level \Sea" lev"el\ The level of the surface of the sea; any surface on the same level with the sea. [1913 Webster] Sealgh