  Distribution amplitudes are functions of non-perturbative matrix elements
describing the hadronization of quarks and gluons. Thanks to factorization
theorems, they can be used to compute the scattering amplitude of high-energy
processes. Recently, new ideas have allowed their computation using lattice
QCD, which should provide us with a general, fully relativistic determination.
We present the first lattice calculation of the $\eta_c$-meson distribution
amplitude at leading twist. Starting from the relevant matrix element in
discrete Euclidean space on a set of $N_f=2$ CLS ensembles, we explain the
method to connect to continuum Minkowski spacetime. After addressing several
sources of systematic uncertainty, we compare to Dyson-Schwinger and
non-relativistic QCD determinations of this quantity. We find significant
deviations between the latter and our result even at small Ioffe times.
