plain sailing vs procession

plain sailing and procession both are nouns.

Word	Noun	Adjective	Verb	Adverb
plain sailing	Yes	No	No	No
procession	Yes	No	No	No

As nouns, procession is a hypernym of plain sailing; that is, procession is a word with a broader meaning than plain sailing:

Other hypernyms of plain sailing include advance, advancement, forward motion, onward motion, progress, progression.

plain sailing (noun)	procession (noun)
easy unobstructed progress	the group action of a collection of people or animals or vehicles moving ahead in more or less regular formation
	the act of moving forward (as toward a goal)
	(theology) the origination of the Holy Spirit at Pentecost