1) One-foot line of verse 2) Type of verse 
In poetry, a monometer is a line of verse with just one metrical foot, exemplified by this portion of Robert Herrick`s `Upon His Departure Hence`: ...
one foot; sometimes termed monopody, a single foot, one measure made up of one foot. For example, the well-known Madam, I'm Adam. or two central lines of each stanza in George Herbert's 'Easter Wings.'
• (n.) A rhythmic series, consisting of a single meter.
a rare form of verse in which each line consists of a single metrical unit (a foot or dipody). The best-known example of an entire poem in monometer ... [1 related articles]
One foot
Mo·nom'e·ter noun [ Greek ... of one meter; 
A line consisting of one metrical foot. Monometers are very rare. However an example of a (predominantly) iambic monometer is Upon His Departure Hence by Robert Herrick.Â
a line of verse of one measure or foot.