Demur, scruple, balk, jib, shy, boggle, stick, stickle, strain are comparable when they mean to hesitate or show reluctance because of difficulties in the way.
One demurs to or at something when one raises objections to it, casts doubt upon it, or takes exception to it, thereby interposing obstacles which delay action, procedure, or decision.
In modern use the emphasis is commonly on objection.
One scruples to do or at doing something when he is reluctant because his conscience bothers or because he is doubtful of the propriety, expediency, or morality of the action; the word is increasingly common in a negative construction.
One balks (often at something) when he stops short and obstinately refuses to go further in his course because he has reached the limit of strength, courage, credulity, or tolerance .
One jibs (often at something) when he balks like a horse and backs away or out.
One shies at, away from, or off from something when like a suddenly frightened horse he recoils or swerves aside in alarm or distaste or suspicion and is unable to proceed or act.
One boggles at, over, or about something from which he by temperament, instinct, or training shies away. In addition, boggle often implies scrupling or fussing.
One sticks at something to which he demurs because of scruples, especially scruples of conscience; the term is used frequently in the idiom "stick at nothing," which is another way of saying be absolutely unscrupulous.
One stickles at, about, or over something to which he demurs or raises objections because it is offensive, distasteful, or contrary to his principles.
One strains at something when he demurs to it as beyond his power to believe, accept, understand, or do. This usage is chiefly dependent on the scriptural passage "ye blind guides, which strain at a gnat, and swallow a camel." The object of at is commonly something which might without real difficulty be believed, accepted, understood, or done.