The core root of this name means to "attract" and "possess" in old-Russian ("vad"it'). So the bearer of this name is essentially someone who attracts people and is loved by them or just a popular person-magnet.
A Czech handbook on names, by Miroslava Knappová, claims it could mean "maligned". But I guess it's not a source of much significance, when it itself says it's "possibly".
Vadim is a unique name, NOT a truncation of Vladimir. Vadim comes from the Slavic vedet. It still exists in Czech, Polish but it is mainly popular in Russia. (Slavic meaning) "A powerful ruler" and in addition "the knowing one" (Greek meaning) "deceiving and unpredictable"
― Anonymous User 6/16/2006
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Very old Slavic name meaning "driven by something".