communication by exchange of letters.

a letter or letters that pass between correspondents

It will take me all day to answer this business correspondence.

Also, correspondency. an instance of corresponding.

similarity or analogy.

agreement; conformity.

news, commentary, letters, etc., received from a newspaper or magazine correspondent.

Mathematics . function ( def. 4a ) .

noun

difference , disagreement

noun

accord , analogy , coherence , coincidence , comparability , comparison , concurrence , conformity , congruity , consistency , correlation , equivalence , fitness , harmony , likeness , match , regularity , relation , resemblance , similarity , symmetry , exchange of letters , letters , mail , messages , post , reports , writing , accordance , chime , conformance , conformation , congruence , harmonization , keeping , affinity , alikeness , parallelism , similitude , uniformity , uniformness , adaptation , agreement , epistle , homology