inlet vs fiord

inlet and fiord both are nouns.

Word	Noun	Adjective	Verb	Adverb
inlet	Yes	No	No	No
fiord	Yes	No	No	No

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

inlet: an arm off of a larger body of water (often between rocky headlands)
fiord: a long narrow inlet of the sea between steep cliffs; common in Norway

Other hyponyms of inlet include cove, fjord, loch.

inlet (noun)	fiord (noun)
an opening through which fluid is admitted to a tube or container	a long narrow inlet of the sea between steep cliffs; common in Norway
an arm off of a larger body of water (often between rocky headlands)