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In this paper we present a detailed study of the giant radio halo in thegalaxy cluster Abell 697, with the aim to constrain its origin and connectionwith the cluster dynamics. We performed high sensitivity GMRT observations at325 MHz, which showed that the radio halo is much brighter and larger at thisfrequency, compared to previous 610 MHz observations. In order to derive theintegrated spectrum in the frequency range 325 MHz--1.4 GHz, we re--analysedarchival VLA data at 1.4 GHz and made use of proprietary GMRT data at 610 MHz.{Our multifrequency analysis shows that the total radio spectrum of the giantradio halo in A\,697 is very steep, with $\alpha_{\rm~325 MHz}^{\rm~1.4 GHz}\approx 1.7-1.8$. %\pm0.1$. Due to energy arguments, a hadronic origin of thehalo is disfavoured by such steep spectrum. Very steep spectrum halos inmerging clusters are predicted in the case that the emitting electrons areaccelerated by turbulence, observations with the upcoming low frequency arrayswill be able to test these expectations.}

The very steep spectrum radio halo in Abell 697