  CeCd$_3$As$_3$ is a rare-earth triangular-lattice antiferromagnet with large
inter-layer separation. Our field-dependent heat capacity measurements at
dilution fridge temperatures allow us to trace the field-evolution of the
spin-excitation gaps throughout the antiferromagnetic and paramagnetic regions.
The distinct gap evolution places strong constraints on the microscopic
pseudo-spin model, which, in return, yields a close {\it quantitative}
description of the gap behavior. This analysis provides crucial insights into
the nature of the magnetic state of CeCd$_3$As$_3$, with a certainty regarding
its stripe order and low-energy model parameters that sets a compelling
paradigm for exploring and understanding the rapidly growing family of the
rare-earth-based triangular-lattice systems.
