attention vs observance

attention and observance both are nouns.

Word	Noun	Adjective	Verb	Adverb
attention	Yes	No	No	No
observance	Yes	No	No	No

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

attention: the process whereby a person concentrates on some features of the environment to the (relative) exclusion of others
observance: the act of noticing or paying attention

Other hyponyms of attention include attentiveness, heed, paying attention, regard, clock-watching, ear, eye, notice, observation, notice.

attention (noun)	observance (noun)
the work of providing treatment for or attending to someone or something	the act of observing; taking a patient look
a courteous act indicating affection	conformity with law or custom or practice etc.
a motionless erect stance with arms at the sides and feet together; assumed by military personnel during drill or review	the act of noticing or paying attention
the process whereby a person concentrates on some features of the environment to the (relative) exclusion of others	a formal event performed on a special occasion
the faculty or power of mental concentration
a general interest that leads people to want to know more