stiff

noun 0.598

straight face

noun 0.580

stoicism

noun 0.571

stiffy

noun 0.560

stiffness

noun 0.558

unflappability

noun 0.536

stoic

noun 0.534

stiffening

noun 0.533

poker face

noun 0.531

sangfroid

noun 0.525

straight bat

noun 0.522

stuffed shirt

noun 0.518

toughness

noun 0.516

sternness

noun 0.516

stifle

noun 0.512

stubbornness

noun 0.510

uptight

noun 0.503

fortitude

noun 0.502

tough nut to crack

noun 0.501