These words refer to the act of hanging back from full participation or full assent. Demur suggests mild dissent or personal objection, possibly in reply to a direct request: gently demurring to her notion of leaving the party early. It may also imply hesitation prompted by doubt or indecision: Though urged to stay to dinner, she still politely demurred . Demur , in comparison with the other words in this set, might now seem too stiffly formal. Scruple , closely related to demur and only a little less formal, points specifically to hesitation or objection on moral or ethical grounds.

• A single girl of that era often scrupled about being left alone with a gentleman; He did not scruple to tell lies when it served his interests.

The verb scruple might now especially apply to over-fussy or niggling from shy . Shy emphasizes instead a skittish starting aside or squeamish holding back out of fear, doubt or caution. It thus suggests a more intense negation than demur or scruple , pointing to a reaction based less on reflection than on instinct.

• The horse shied at the first hiss of the snake; The girl shied away from looking the strange man in the eye.

Recoil and shrink relate more closely to shy than to demur or scruple . Recoil suggests a sudden springing back out of surprise, distaste or fear. Shrink does not carry the implication of suddenness but emphasizes an indecisive cringing from something ominous, frightening or even disgusting.

• She shrank from entering the grimy bar with him but once inside, she recoiled at every depraved face that met her gaze.

Shrink may also suggest excessive timidity: a shrinking violet.

Balk suggests a holding back that is more determined than shrink , but not necessarily sudden, as with recoil and shy . The determination implied by balk , in fact, extends to downright stubbornness: workers who simply balked at the poor conditions in the factory. The word also has a special overtone implying that the subject has put up with a situation as long as possible, but now makes a defiant stand as a result of weariness or anger.

• They balked at going another step until their guide agreed to name a fee for his services; The donkey balked at climbing the next hill until he had food and water.

Boggle , by contrast, implies a refusal at the outset, triggered by disbelief, shock or amazement. In one sense, it is an intensification of recoil : Cabinet members who boggled at the Prime Minister’s astonishing proposal; the mind boggle at such an idea.

Shirk has a special sense that separates it sharply from these other words. The holding back, here, is simply an expression of laziness or unwillingness to co-operate: teachers who shirk the responsibilities they have to their students.