What is "to gain upon"

Gain \Gain\, v. i. To have or receive advantage or profit; to acquire gain; to grow rich; to advance in interest, health, or happiness; to make progress; as, the sick man gains daily. Thou hast greedily gained of thy neighbors by extortion. --Ezek. xxii. 12. Gaining twist, in rifled firearms, a twist of the grooves, which increases regularly from the breech to the muzzle. To gain on or To gain upon.

1. To encroach on; as, the ocean gains on the land.

2. To obtain influence with.

3. To win ground upon; to move faster than, as in a race or contest.

4. To get the better of; to have the advantage of.

   The English have not only gained upon the Venetians in the Levant, but have their cloth in Venice itself.
   --Addison.

   My good behavior had so far gained on the emperor, that I began to conceive hopes of liberty.
   --Swift.