Pressure line like this found in one pub (6)
I believe the answer is:
isobar
'pressure line' is the definition.
(I've seen this before)
'like this found in one pub' is the wordplay.
'like this' becomes 'so'.
'found in' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'pub' becomes 'bar' (I've seen this before).
'i'+'bar'='ibar'
'so' inserted within 'ibar' is 'ISOBAR'.
(Other definitions for isobar that I've seen before include "depression indicator?" , "It appears on some maps" , "Line showing points having equal barometric pressure at a given time" , "meteorologist's line" , "Line on map showing atmospheric pressure" .)