headache vs bugaboo

headache and bugaboo both are nouns.

Word	Noun	Adjective	Verb	Adverb
headache	Yes	No	No	No
bugaboo	Yes	No	No	No

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

Other hyponyms of headache include burden, encumbrance, incumbrance, load, onus, business.

headache (noun)	bugaboo (noun)
something or someone that causes anxiety; a source of unhappiness	a source of concern
pain in the head caused by dilation of cerebral arteries or muscle contractions or a reaction to drugs	an imaginary monster used to frighten children