Definition of isobar noun from the Oxford Advanced Learner's Dictionary

 

isobar

 noun
noun
BrE BrE//ˈaɪsəbɑː(r)//
 
; NAmE NAmE//ˈaɪsəbɑːr//
 
(specialist)
 
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a line on a weather map that joins places that have the same air pressure at a particular time Word Origin mid 19th cent.: from Greek isobaros ‘of equal weight’, from isos ‘equal’ + baros ‘weight’.
See the Oxford Advanced American Dictionary entry: isobar