I thank you for your kindness, but I had already consulted the
MacBain's Dictionary. The problem is that I do not find reliable that
OIr. gann < *gando-s is linked with O.Ind. gandha/yate "hurt", Lit.
gendu\ "be injured". These terms derive from *ghwen- (the radical 'a'
is found in Arm. gan "injure, hurt" and Alb. gand "hurt, offense") as
well as OIr. gonim and MW. gwanu (see e. g. Kim McCone, "Towards a
relative Chronology of ancient and medieval Celtic sound change",
1996). Therefore I can't believe that the same Celtic root yielded
'gonim' and 'gann'. Besides I am very sceptic about a semantic shift
"hurt, injure" > "(to get or make) scarce, thin".
As the letter G of the "Lexique etymologique de l'irlandais ancien"
is not yet published and as I cannot consult here all the revews on
Celtic old languages, I should like to know if some scholar after Mac
Bain suggested different etymologies.