  We present spectroscopic and photometric data of the Type Ibn supernova (SN)
2014av, discovered by the Xingming Observatory Sky Survey. Stringent
pre-discovery detection limits indicate that the object was detected for the
first time about 4 days after the explosion. A prompt follow-up campaign
arranged by amateur astronomers allowed us to monitor the rising phase (lasting
10.6 days) and to accurately estimate the epoch of the maximum light, on 2014
April 23 (JD = 2456771.1 +/- 1.2). The absolute magnitude of the SN at the
maximum light is M(R) = -19.76 +/- 0.16. The post-peak light curve shows an
initial fast decline lasting about 3 weeks, and is followed by a slower decline
in all bands until the end of the monitoring campaign. The spectra are
initially characterized by a hot continuum. Later on, the temperature declines
and a number of lines become prominent mostly in emission. In particular, later
spectra are dominated by strong and narrow emission features of He I typical of
Type Ibn supernovae (SNe), although there is a clear signature of lines from
heavier elements (in particular O I, Mg II and Ca II). A forest of relatively
narrow Fe II lines is also detected showing P-Cygni profiles, with the
absorption component blue-shifted by about 1200 km/s. Another spectral feature
often observed in interacting SNe, a strong blue pseudo-continuum, is seen in
our latest spectra of SN 2014av. We discuss in this paper the physical
parameters of SN 2014av in the context of the Type Ibn supernova variety.
