Wild boars following one line of pressure (6)
I believe the answer is:
isobar
'line of pressure' is the definition.
'isobar' can be an answer for 'line' (isobar is a kind of line). I'm unsure of the 'of pressure' bit.
'wild boars following one' is the wordplay.
'wild' indicates anagramming the letters.
'following' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'boars' with letters rearranged gives 'sobar'.
'sobar' after 'i' is 'ISOBAR'.
Can you help me to learn more?
(Other definitions for isobar that I've seen before include "Line on map indicating barometric pressure" , "Line on map connecting places of equal atmospheric pressure" , "sign of pressure" , "It appears on some maps" , "Map line showing atmosphere pressure" .)