Abarim Publications' online Biblical Greek Dictionary
The ubiquitous preposition συν (sun) expresses a close connection, a joined activity, shared situation or maintained coalition, and can usually be translated as: with or together with. It differs from the preposition μετα (meta) in that the latter expresses a mere proximity while συν (sun) expresses an intimate relation.
Our preposition is frequently used to indicate cooperative bonds in society (sit with, stand with, be with, talk with, walk with, etcetera) but it may also be used to indicate the help, inspiration or instruction from someone (or something). It comes with only the dative case, which suggests that this particle mostly describes about a motion towards unity rather than a motion deriving from unity.
Our particle may express the "seen-from-all-sides" or "on-all-accounts", that is wholesale completion of an activity or process, and may, with verbs that already express completion, hence serve as an intensive.