The acoustic-phonon emission from monolayer molybdenum disulfide (ML-MoS2) driven by a direct-current electric field is studied theoretically by using the Boltzmann equation method. It is found that Cerenkov emission of terahertz acoustic-phonons can be generated when a very weak electric field is applied to ML-MoS2. The physical mechanisms of acoustic-phonon emission are analyzed from the perspective of condensed matter physics. The acoustic-phonon emission from ML-MoS2 is also compared with those from graphene and GaAs. The results reveal that the frequencies of acoustic-phonons generated from ML-MoS2 are between the frequencies of those generated from GaAs and graphene. The results of this work suggest that ML-MoS2 can make up for graphene and GaAs in respect of acoustic-phonon emission and be used in tunable hypersonic devices such as terahertz sound sources.