I always thought ‘grian’ was the sun in Scots Gaelic - a name I use for lesser celandine. The spelling ‘gruen’ seems strange to me for sun. I ain’t no gaelic scholar but others in the family are learning.
MacBains dictionary http://www.ceantar.org/Dicts/MB2/mb22.html
grian
sun, Irish, Old Irish grían: *greinâ, @ghr-einâ, root @gher, warm, as in gar. Cf. Sanskrit ghr@.n@.is, sunshine, ghramsa, heat; Welsh greian, what gives heat, sun. See further under grìos. Hence grianan, sunny place, summer house, solarium of Latin, from sol, sun.
grùthan , grùan
liver, Irish aeu. grúan (Lh. (Comp.Voc. sub “jecur”): *grûso-: root ghru, gritty, of grothlach.
Maybe Daniel has a thing for liver - sorry that joke was offal…
gràinne
a grain, small quantity, Irish gráinne, Old Irish gráinne, granulum, grán, granum, Welsh grawn, Cornish gronen, Breton greun, (pl.): *grâno-; Latin grânum (*gr@-@.no-); English corn (Stokes). Some hold that the Celtic is borrowed from the Latin.
or short of stature