mo vs blink of an eye

mo and blink of an eye both are nouns.

Word	Noun	Adjective	Verb	Adverb
mo	Yes	No	No	No
blink of an eye	Yes	No	No	No

As nouns, blink of an eye is a hyponym of mo; that is, blink of an eye is a word with a more specific, narrower meaning than mo:

mo: an indefinitely short time
blink of an eye: a very short time (as the time it takes the eye to blink or the heart to beat)

Other hyponyms of mo include flash, heartbeat, instant, jiffy, New York minute, split second, trice, twinkling, wink.

mo (noun)	blink of an eye (noun)
an indefinitely short time	a very short time (as the time it takes the eye to blink or the heart to beat)