It will be some form of diode.
Could be a Zener or TVS (transient suppression diode). The very low forward voltage suggests a Schottky diode, however your measurements could be skewed by the rest of the circuit, plus no idea what current your measurement is passing through the diode. Measuring the reverse voltage would be interesting, but that would be risky.
Zener is quite likely based on the circuit.
Based on the dimensions, you have a SOD123 package (typically 1.55mm x 2.65mm).
Decoding the marking is difficult without knowing more about the part. For example, BD could make it a 7.5V Zener diode (PDZ7.5BGW). Alternatively, WL could be a 15V Zener diode (BZT52C15).
A very likely candidate is a Diodes Inc. 18V Zener, specifically BZT52C18. From the datasheet it is marked as follows:
Notice the orientation of the markings.
First you have the bar as expected.
Then a two digit code. In your case "WL" which corresponds to 18V per the following excerpt from the full table:
Then you have a two digit date code placed at a 90 degree angle. In your case BD which decodes as 2014 (B) December (D).