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Webster 1913 Edition

Adj.

Habitually attacking, harassing, or pressing upon or about;

as, a

besetting

sin

ppr.

Surrounding; besieging; waylaying.

Adj.

Habitually attending, or pressing; as a besetting sin.

besetting

besetting ‎(plural besettings)

The act of one who besets or attacks.
- John Bunyan
  I might also here tell you of the contests and battles that such are engaged in, wherein they find the besettings of Satan, above any other of the saints.