dig in

verb

1. military to create (a defensive position) by digging foxholes, trenches, etc

2. informal,  to entrench (oneself) firmly

3. informal,  (intr) to defend or maintain a position firmly, as in an argument

4. informal,  (intr) to begin vigorously to eat

   don't wait, just dig in

5. informal,  to refuse stubbornly to move or be persuaded

Idioms and Phrases

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]

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]

Begin to work intensively, as in If we all dig in it'll be done before dark. [ Colloquial ; second half of 1800s]

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]