line of force is a noun meaning "an imaginary line in a field of force; direction of the line at any point is the direction of the force at that point". It carries one recorded sense.
an imaginary line in a field of force; direction of the line at any point is the direction of the force at that point
Definitions, synonyms and semantic relations for line of force come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.