The correct answer is (A) To fortify by surrounding with a trench; to dig protective trenches. To surround or protect with a trench; to settle (oneself) securely, as in a job or some other position considered to be safe;

Entrench comes from Latin truncare (to cut).

Examples of use:

• The enemy soldiers are entrenched on this side of the closest hill.
• He was safely entrenched behind an undisputable alibi.