Synonyms for Fathom (same or very similar meaning)
WordNet sense 1 (a linear unit of measurement (equal to 6 feet) for water depth):
fthmWordNet sense 2 (come to understand):
bottom, penetrateWordNet sense 3 (measure the depth of (a body of water) with a sounding line):
soundFrom the ODE community, based on WordNetadd/edit