dig in

1.  Excavate trenches to defend oneself in battle and hold one's position, as in The battalion dug in and held on. This usage gained currency in the trench warfare of World War I. [Mid-1800s]
2.  Also, dig in one's heels. Adopt a firm position, be obstinate and unyielding. For example, Arthur refused to argue the point and simply dug in, or The dog dug in its heels and refused to move. [Colloquial; late 1800s]
3.  Begin to work intensively, as in If we all dig in it'll be done before dark. [Colloquial; second half of 1800s]
4.  Also, dig into. Begin to eat heartily, as in Even before all the food was on the table they began to dig in, or When the bell rang, the kids all dug into their lunches. [Colloquial; early 1900s]

Definition: begin with enthusiasm
Antonyms: avoid, delay, postpone, procrastinate

The verb has 2 meanings:

Meaning #1: occupy a trench or secured area
  Synonym: entrench

Meaning #2: eat heartily
  Synonym: pitch in