fist
The word shimatteru means that something is closed.
Classroom is a closed compound word.
Both closed.
Paper is a closed syllable word.
Swadling is and English verb which means wrapping tightly in garments or cloth. It is primarily used describing a baby wrapped in a receiving blanket.
Yes, the word 'fist' is a noun, a singular, common, concrete noun; a word for a hand with tightly closed fingers, a word for a thing. The word 'fist' is also a verb; to strike or grasp with a clenched hand.
The word that means 'stretched tightly' is taut.
The word is clutch. Note that this is a verb and a noun at the same time.
to push
The word clenching means to tightly grip your hand or hands, to close or squeeze together or to clinch a bolt. Mostly it is referred to when using your hands.
jam
A word that would mean the same as gripping tightly could be Grasp or Cluch/Clench.
taut as in the rope was pulled taut
grip or cling
You could say, "Her lips were pursed." It means her lips were tightly closed.
The word manu means hand.
I used all the force I could to pry open the tightly closed lid on the pickle jar.