bank up

present singular third person banks up · participle present banking up · participle past banked up · past banked up

1. To press a mound of something against something else.
2. To make a mound to guard against something.
3. intransitiveTo bank (form a bank; gather in masses).

   ... ominous clouds banking up and darkening the sky behind them.

   2022 September 16, Boyd Cable, Front Lines, DigiCat

   2 more examples

   Next, heavy soft clouds, banking up till the sky becomes overcast, are recorded, easily recognised by their lowering appearance, due to the dampness of the air, which also causes them to reflect the glare of large fires or the lights of cities[…]

   1893, Henry Newton Dickson, Meteorology: The Elements of Weather and Climate, page 10

   Then turning: "There'll be more rain," he said, "you can see the clouds banking up to the North-West, larger than these."

   1920, Elliot Lovegood Grant Watson, Deliverance, page 143

   Synonyms: fortify