tower of strength vs pillar of strength

tower of strength and pillar of strength both are nouns.

Word	Noun	Adjective	Verb	Adverb
tower of strength	Yes	No	No	No
pillar of strength	Yes	No	No	No

As nouns, tower of strength and pillar of strength are synonyms defined as:

tower of strength and pillar of strength: a person who can be relied on to give a great deal of support and comfort

tower of strength (noun)	pillar of strength (noun)
a person who can be relied on to give a great deal of support and comfort	a person who can be relied on to give a great deal of support and comfort