under, i.e. (with the genitive case) of place (beneath), or with verbs (the agency or means, through); (with the accusative case) of place (whither (underneath) or where (below) or time (when (at))

by implication, to try, condemn, punish

undissembled, i.e. sincere

to act hypocritically in concert with

acting under a feigned part, i.e. (figuratively) deceit ("hypocrisy")

an actor under an assumed character (stage-player), i.e. (figuratively) a dissembler ("hypocrite"