'Running board' definitions:

Definition of 'running board'

noun

A narrow footboard serving as a step beneath the doors of some old cars

From: GCIDE

Running \Run"ning\, a.
1. Moving or advancing by running. Specifically, of a horse: (a) Having a running gait; not a trotter or pacer. (b) trained and kept for running races; as, a running horse. --Law. [1913 Webster]
2. Successive; one following the other without break or intervention; -- said of periods of time; as, to be away two days running; to sow land two years running. [1913 Webster]
3. Flowing; easy; cursive; as, a running hand. [1913 Webster]
4. Continuous; keeping along step by step; as, he stated the facts with a running explanation. "A running conquest." --Milton. [1913 Webster]
What are art and science if not a running commentary on Nature? --Hare. [1913 Webster]
5. (Bot.) Extending by a slender climbing or trailing stem; as, a running vine. [1913 Webster]
6. (Med.) Discharging pus; as, a running sore. [1913 Webster]
Running block (Mech.), a block in an arrangement of pulleys which rises or sinks with the weight which is raised or lowered.
Running board, a narrow platform extending along the side of a locomotive. [1913 Webster]