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We present observations of the possible short GRB 180418A in $\gamma$-rays,X-rays, and in the optical. Early optical photometry with the TAROT and RATIRinstruments show a bright peak ($\approx$ 14.2 AB mag) between $T+28$ and$T+90$ seconds that we interpret as the signature of a reversal shock. Laterobservations can be modeled by a standard forward shock model and show noevidence of jet break, allowing us to constrain the jet collimation to$\theta_j> 7^\circ$. Using deep late-time optical observations we place anupper limit of $r>24$ AB mag on any underlying host galaxy. The detection ofthe afterglow in the \textit{Swift} UV filters constrains the GRB redshift to$z<1.3$ and places an upper bound on the $\gamma$-ray isotropic equivalentenergy $E_{\rm{\gamma,iso}} < 3 \times 10^{51}$ erg.  The properties of this GRB (e.g. duration, hardness ratio, energetic, andenvironment) lie at the intersection between short and long bursts, and we cannot conclusively identify its type. We estimate that the probability that it isdrawn from the population of short GRBs is 10\%-30\%.

Reverse Shock Emission Revealed in Early Photometry in the Candidate Short GRB 180418A