pillar of strength vs tower of strength

pillar of strength and tower of strength both are nouns.

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

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

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

pillar of strength (noun)	tower 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