Nouns

(n)stiffan ordinary man“a lucky stiff”, “a working stiff”
(n)cadaver, corpse, stiff, clay, remainsthe dead body of a human being“the cadaver was intended for dissection”, “the end of the police search was the discovery of a corpse”, “the murderer confessed that he threw the stiff in the river”, “honor comes to bless the turf that wraps their clay”

Adjectives

(s)stiffnot moving or operating freely“a stiff hinge”
(s)stiffstrong, vigorous“a stiff current”, “a stiff breeze”
(s)starchy, stiff, buckramrigidly formal“a starchy manner”, “the letter was stiff and formal”, “his prose has a buckram quality”
(a)potent, strong, stiffhaving a strong physiological or chemical effect“a potent toxin”, “potent liquor”, “a potent cup of tea”, “a stiff drink”
(s)firm, steadfast, steady, stiff, unbendable, unfaltering, unshakable, unwaveringmarked by firm determination or resolution; not shakable“firm convictions”, “a firm mouth”, “steadfast resolve”, “a man of unbendable perseverance”, “unwavering loyalty”
(s)rigid, stiffincapable of or resistant to bending“a rigid strip of metal”, “a table made of rigid plastic”, “a palace guardsman stiff as a poker”, “stiff hair”, “a stiff neck”

Adverbs

(r)stiffto a great degree“bored stiff”, “frightened stiff”
(r)stiffly, stiffin a stiff manner“his hands lay stiffly”