If using the Zener method, as noted earlier this is done in pairs. The total voltage drop is the sum of the two diodes. At any given time, one of the diodes is dropping the Zener voltage (e.g. 5.1V) and the other is dropping about 0.7V... in this case the sum being almost 6V.
If you only want to drop 5V (from 14 down to 9), you might consider a lower Zener voltage...such as a 4.7V, 4.3V, or even 3.9V. All the same price, all sold by DigiKey (and others of course). As GRJ points out choosing with suitable power-handling capability (Watts) is required.
Note that you can get MORE drop by adding more diodes. But if you go with the pair of Zener diodes, you can't get LESS drop after the fact. Hence another reason to consider something less than 5.1V.
Additionally, nothing stops you from mixing/matching a pair of 5 Watt Zener diodes with one or more pairs of inexpensive 3A diodes allowing fine-tuning of the voltage drop in ~0.7V steps. If buying from DigiKey, you'll be paying way more for shipping than the parts...so minds as well toss some into the order.
Here's a recycled photo from an earlier OGR thread illustrating how a pair of Zener diodes can do the bulk of the voltage drop...and then be augmented with diodes and/or bridge rectifiers to fine-tune the voltage drop.
