morale booster vs encouragement

morale booster and encouragement both are nouns.

Word	Noun	Adjective	Verb	Adverb
morale booster	Yes	No	No	No
encouragement	Yes	No	No	No

As nouns, encouragement is a hypernym of morale booster; that is, encouragement is a word with a broader meaning than morale booster:

Other hypernyms of morale booster include boost.

morale booster (noun)	encouragement (noun)
anything that serves to increase morale	the act of giving hope or support to someone
	the expression of approval and support
	the feeling of being encouraged