screen vs riddle

screen and riddle both are nouns.

Word	Noun	Adjective	Verb	Adverb
screen	Yes	No	Yes	No
riddle	Yes	No	Yes	No

As nouns, riddle is a hyponym of screen; that is, riddle is a word with a more specific, narrower meaning than screen:

screen: a strainer for separating lumps from powdered material or grading particles
riddle: a coarse sieve (as for gravel)

Other hyponyms of screen include sifter, dirt sifter, soil sifter.

As verbs, screen and riddle are synonyms defined as:

screen (noun)	riddle (noun)
a protective covering consisting of netting; can be mounted in a frame	a coarse sieve (as for gravel)
a covering that serves to conceal or shelter something	a difficult problem
a strainer for separating lumps from powdered material or grading particles
partition consisting of a decorative frame or panel that serves to divide a space
a protective covering that keeps things out or hinders sight
the display that is electronically created on the surface of the large end of a cathode-ray tube
a white or silvered surface where pictures can be projected for viewing
the personnel of the film industry

screen (verb)	riddle (verb)
examine methodically	explain a riddle
protect, hide, or conceal from danger or harm	set a difficult problem or riddle
prevent from entering	speak in riddles
separate with a riddle, as grain from chaff	pierce with many holes
project onto a screen for viewing	separate with a riddle, as grain from chaff
examine in order to test suitability	spread or diffuse through
test or examine for the presence of disease or infection