means To take small, gentle bites of food, or to make tentative, partial moves toward something larger.

from From Middle Low or Middle Dutch roots — a cousin of words like 'nibbelen' — that carried the sense of pecking or gnawing in tiny amounts. It's almost certainly related to 'nib' and 'neb,' words for a beak or pointed tip, which makes a kind of sense: a nibble is the work of a small sharp mouth, taking only what the very point can reach. The word entered English around the 1400s and has been quietly chewing at the edges of things ever since.