( n. )
A unit employed by oculists in numbering glasses according to the metric system; a refractive power equal to that of a glass whose principal focal distance is one meter.
( n. )
A unit employed by oculists in numbering glasses according to the metric system; a refractive power equal to that of a glass whose principal focal distance is one meter.
Webster's Revised Unabridged English Dictionary. Пересмотренный полный словарь английского языка Webster. 2012