Noun | 1. | fthm - a linear unit of measurement (equal to 6 feet) for water depth linear measure, linear unit - a unit of measurement of length |
2. | fthm - (mining) a unit of volume (equal to 6 cubic feet) used in measuring bodies of ore mining, excavation - the act of extracting ores or coal etc from the earth capacity measure, capacity unit, cubage unit, cubature unit, cubic content unit, cubic measure, displacement unit, volume unit - a unit of measurement of volume or capacity |