  Today it is widely believed that $s$-channel excitation of an on-shell~$W$
boson, commonly known as the Glashow resonance, can be initiated in matter only
by the electron antineutrino in the process $\bar\nu_ee^-\rightarrow W^-$ at
the laboratory energy around~6.3~PeV. In this paper we argue that the Glashow
resonance within the Standard Model also occurs in neutrino--nucleus
collisions. The main conclusions are as follows. 1)~The Glashow resonance can
be excited by both~neutrinos and~antineutrinos of all the three flavors
scattering in the Coulomb field of a nucleus. 2)~The Glashow resonance in a
neutrino--nucleus reaction does not manifest itself as a Breit--Wigner-like
peak in the cross section but the latter exhibits instead a slow
logarithmic-law growth with the neutrino energy. The resonance turns thus out
to be hidden. 3)~More than~$98\%$ of~$W$ bosons produced in the sub-PeV region
in neutrino-initiated reactions in water/ice will be from the Glashow
resonance. 4)~The vast majority of the Glashow resonance events in a neutrino
detector is expected at energies from a few TeV to a few tens of TeV, being
mostly initiated by the conventional atmospheric neutrinos dominant in this
energy range. Calculations of the cross sections for Glashow resonance
excitation on the oxygen nucleus as well as on the proton are carried out in
detail. The results of this paper can be useful for studies of neutrino
interactions at large volume water/ice neutrino detectors. For example, in the
IceCube detector one can expect~0.3 Glashow resonance events with shower-like
topologies and the deposited energies above~$300~\text{TeV}$ per year. It is
therefore likely already to have at least one Glashow resonance event in the
IceCube data set.
