Adverb (fukushi), Noun which may take the genitive case particle 'no', Na-adjective (keiyodoshi)
a little; a bit; somewhat; slightly; rather
Usually written using kana alone
ここだけの話だが、彼はいささか間が抜けている。Between you and me, he is rather stupid.
Also written 聊か【いささか】、些【いささか】、聊【いささか】