The Collaborative International Dictionary
Isobront
Isobront \I"so*bront\ ([imac]"s[-o]*br[o^]nt), n. [Iso- + Gr. bronth` thunder.] (Meteor.) An imaginary line, or a line on a chart, marking the simultaneous development of a thunderstorm, as noted by observing the time when the thunder is heard at different places.
Wiktionary
isobront
n. A line drawn through geographical points at which a given phase of thunderstorm activity occurred simultaneously.