Bitter :

Answer: Option D

Blunt : bovine, obtuse, lotus flower, thickheaded, thickskulled.
Bold : daring, courageous, perky, impudent, daredevil.
Timid : sneaky, fainthearted, shy, recreant, poor-spirited.
Sweet : sugary, sisterly, dulcet, mawkish, unleavened.
Bitter : bitterish, sore

Antonym of Bitter is Sweet.