casuistry vs line of reasoning

casuistry and line of reasoning both are nouns.

Word	Noun	Adjective	Verb	Adverb
casuistry	Yes	No	No	No
line of reasoning	Yes	No	No	No

As nouns, line of reasoning is a hypernym of casuistry; that is, line of reasoning is a word with a broader meaning than casuistry:

casuistry: argumentation that is specious or excessively subtle and intended to be misleading
line of reasoning: a course of reasoning aimed at demonstrating a truth or falsehood; the methodical process of logical reasoning

Other hypernyms of casuistry include argument, argumentation, line, logical argument.

casuistry (noun)	line of reasoning (noun)
moral philosophy based on the application of general ethical principles to resolve moral dilemmas	a course of reasoning aimed at demonstrating a truth or falsehood; the methodical process of logical reasoning
argumentation that is specious or excessively subtle and intended to be misleading