In obsolete|lang=en terms the difference between compassion and expediency
is that
compassion is (obsolete) to pity while
expediency is (obsolete) haste; dispatch.
As nouns the difference between compassion and expediency
is that
compassion is deep awareness of the suffering of another, coupled with the wish to relieve it while
expediency is (uncountable) the quality of being fit or suitable to effect some desired end or the purpose intended; suitability for particular circumstance or situation.
As a verb compassion
is (obsolete) to pity.