An Etymological Dictionary of the German Language/Blatt
Blatt, n., ‘leaf, blade, newspaper,’ from the equiv. MidHG. and OHG. blat n.’; comp. the corresponding Du. blad, AS. blœd, ‘leaf,’ E. blade; Goth. *blaþ. The dental of these cognates seems to be a suffix; bla- from pre-Teut. bhlo-, as well as Lat. fol-ium, Gr., φύλλον, ‘leaf,’ may have been formed from a root bhol, bhlô. It is uncertain whether Goth. *blada- is really a partic. with an Ayran suffix tó-, with the meaning ‘having ceased to bloom’ or ‘fully grown.’ See blühen.