愚姉 is read as ぐし (gushi) and means older sister.
ぐし
gushi
ぐち
moha (ignorance, folly)
おろか
foolish
ぐれんたい
gang of young toughs
ぐ
I
ぐこう
foolish act
ぐちょく
simple honesty
ぐみんせいさく
policy of keeping the people ignorant and easily subjugated
ぐこうやまをうつす
where there's a will, there's a way
ぐもんぐとう
silly questions and silly answers
ぐじん
fool
ぐけん
one's humble opinion
ぐみん
ignorant people