Transverse absorption-line spectroscopy has proven to be a vital tool for observing the circumgalactic medium (CGM), but interpretation is complicated by ambiguity in identifying where absorbing gas is located along the sightline, and by the limited number of sightlines available per galaxy. Hydrodynamic simulations have also contributed significantly to our understanding of the CGM, mostly through comparison with observations. In this talk, I discuss an alternative approach - using simulations to interpret observations. Under development, the Circumgalactic Dictionary will be a guide for observers which predicts previously unattainable CGM gas properties given an input spectrum, including temperature, density, metallicity, 3d position and velocity, and information about the gas’s history. The method consists of creating synthetic quasar absorption-line spectra using the IllustrisTNG simulations, deriving observables using a custom-built Voigt profile fitting pipeline, identifying gas along the simulated sightlines that contributed to absorption, and using them to train a Neural Network to map from observables to properties of the simulated CGM absorbing gas. Once completed and publicly released, the Circumgalactic Dictionary will predict probability density functions of physical properties, kinematics, and histories of clouds of absorbing gas, as well as the number of distinct clouds that caused absorption to distinguish between multiphase and multiple cloud scenarios. Built around the framework of Cosmic Origins Spectrograph UV observations, the Circumgalactic Dictionary will provide new insights to existing and future observations.