What is an antonym for billow?

Here are some antonyms for "billow," depending on the context:

For "billow" meaning a large wave:

* Calm

* Still

* Flat

* Smooth

* Serene

For "billow" meaning to swell or rise:

* Shrink

* Contract

* Deflate

* Subside

* Collapse

For "billow" meaning a large quantity of something:

* Shortage

* Deficit

* Scarcity

* Lack

* Minimum

The best antonym depends on the specific meaning of "billow" in your sentence.