When an English speaker refers to an “arrow in the quiver,” they are talking about something that is an additional resource aiding in the achievement of some goal or objective. This sort of phrase is what’s known as a sports metaphor, related to the sport of archery. Arguably, this can also be called a “battle metaphor” related to classic warfare and the use of bows and arrows as weapons.
The origin of the phrase “arrow in the quiver” is not entirely known. Many language experts agree that this phrase must have developed over time as an allegory for the benefits of having ammunition at the ready; a quiver is the cylindrical case archers commonly use to carry their arrows. This metaphor can also be considered a hunting metaphor, where those who hunt with bows and arrows need to have sufficient numbers of arrows at hand to kill and capture their game when spotted.
In most uses of this idiomatic phrase, the speaker is talking about the need to have diverse resources or strategies to handle a challenge or any obstacles to an objective. Most commonly, this idiom represents an extreme abstraction of the idea of having physical arrows in a quiver. For example, if someone says “having good communication skills can be another arrow in your quiver when you go for a job interview,” the “arrow” in the metaphor is in the form of an intangible skill, rather than something concrete that can be stored or used up.
The phrase “arrow in the quiver” is not the only archery metaphor familiar to English speakers. Some also use the phrase “strings to your bow,” and while this may have other meanings, for example, related to stringed instruments like the fiddle, many identify the literal meaning of this phrase as multiple strings in an archery bow. Here, the “strings” in the bow make the bow more resilient and generally stronger.
To contrast the two phrases “arrow in the quiver” and “strings in your bow,” it’s evident that these two idioms work in a very similar way. A well-prepared person might have many arrows in the quiver, in order to avoid running out of “bow shots,” and many strings in the bow to make sure that the bow doesn’t break during archery or hunting. In general, both of these phrases are used to mean “well prepared.”