They grew closer as friends with each passing day.
Meaning: This sentence describes two people becoming closer friends over time.
Choice of Words: "Closer" means nearer in space, time, or relationship. "Passing" means moving from one place to another.
Alternative Expressions
They became better friends with each passing day.
Meaning: This sentence means that the quality of the friendship between the people improved over time.
Choice of Words:They is the subject of the sentence and refers to the people involved in the friendship. Became is a verb that describes the change in the relationship between the friends. Better is an adjective that describes the improved quality of the friendship. Friends is a noun that refers to the relationship between the people. With each passing day is a prepositional phrase that indicates the gradual increase in closeness over time.
Their friendship grew stronger with each passing day.
Meaning: This sentence means that the strength of the friendship between the people increased over time.
Choice of Words:Their is a possessive adjective that indicates that the friendship belongs to the people involved. Friendship is a noun that refers to the relationship between the people. Grew is a verb that describes the gradual increase in strength of the friendship. Stronger is an adjective that describes the increased intensity of the friendship. With each passing day is a prepositional phrase that indicates the gradual increase in strength over time.