  AT2018cow is a unique transient that stands out due to its relatively fast
light-curve, high peak bolometric luminosity, and blue color. These properties
distinguish it from typical radioactively powered core-collapse supernovae
(SNe). Instead, the characteristics are more similar to a growing sample of
Fast Blue Optical Transients (FBOTs). Mostly discovered at hundreds of Mpc,
FBOT follow-up is usually limited to several photometry points and low
signal-to-noise spectra. At only ~60 Mpc, AT2018cow offers an opportunity for
detailed followup. Studies of this object published to date invoke a number of
interpretations for AT2018cow, but none of these specifically consider the
interacting Type Ibn SN subclass. We point out that while narrow lines do not
dominate the spectrum of AT2018cow, as narrow Balmer lines typically do in SNe
IIn, the narrow lines in AT2018cow may nevertheless be a mix of unresolved HII
region emission and emission from slow, pre-shock CSM. We compare AT2018cow to
interacting SNe Ibn and IIn and find a number of noteworthy similarities,
including light-curve rise and fall times, peak magnitude, X-ray light-curves,
and spectroscopic properties. In particular, the He I lines in AT2018cow
closely resemble those in some examples of SNe Ibn or transitional SNe Ibn/IIn
objects. We therefore explore the hypothesis that CSM interaction in a
relatively H-poor system might have some merit in explaining observed
properties of AT2018cow, and we go on to consider progenitor implications for
AT2018cow, FBOTs, and SNe~Ibn.
