Ethics, Morals, Scruples, and Folkways all concern behavior/conduct, and overlap to some extent, but they are not synonyms (I realize that common usage treats the terms "ethics" and "morals" as more or less synonymous, but I contend that they should not be seen as identical in meaning). Adding to the complication involved in distinguishing between these words is the fact that the discipline of Philosophy uses the term "Ethics" to refer to that branch of the tree of Philosophy which deals with the science of conduct, under which header all four of these terms should be placed. I believe this can be resolved by bearing in mind that the use in Philosophy to refer to "the science of conduct" is an example of technical jargon and should be considered an umbrella. So, how do I distinguish these terms, apart from (or rather, under the umbrella of) the technical jargon?
An ethic, or an ethical system, is part of a worldview (be it cultural, philosophical, or religious) and essentially static (although subject to interpretation), thus basically unchanging apart from exegesis and application. Regarding an ethic as more or less objective would not be wrong, although it would be, perhaps, imprecise. To elaborate on this latter notion, I should say that the underlying concepts of an ethic do not themselves change, but the interpretation, and thus, the application, of an ethic may vary over time or due to sectarian differences of perspective; in order to hold this understanding, I must disregard hyper-literalistic legalism, which, I would insist, is an aberration of ethical thought due to the innate irrationality of such a perspective which invariably leads to self-referential incoherence, doublethink, and cognitive dissonance.
A morality is societal, and malleable with respect to time and place, thus relative. Morals change as the society ebbs and flows in its education, experience, technological changes, exposure to other societies, migration, environmental factors, and so on. What is regarded as moral by a given society will change over time, and this change is more than mere reinterpretation and application; the underlying concepts themselves change. If a social group emigrates to another geographic location, the physical environment of their new home, as well as their new neighbors, may affect their morality over time. With technological advances, new challenges arise and new understandings are born, which may alter the underlying moral concepts of the social group. Again, the quality of education in a society fluctuates over time, and this too can change basic concepts of a society.
Scruples are individual viewpoints on conduct and behavior, which are usually influenced to a greater or lesser extent by the morals of the society in which the individual lives, and potentially also by the ethics of the various worldviews with which the individual may have come in contact. Scruples will, for most individuals, change over time due to various influences and experiences, as well as continuing education.
Folkways are either cultural or societal, or both, and tend to be rather conservative, although reasons which were their source may be forgotten or lost over time; while some folkways have an origin in an ethic or a morality, if the original ethical or moral basis be lost or forgotten, they become mere traditional custom and thus are worthy of the name "folkway" for those who (semi-consciously) practice them without understanding of the reason(s) for their existence. An example of this is the practice of walking on one side or the other of a sidewalk/pavement or hallway. Originally, chariot drivers would veer left when meeting, so that the right sides of the chariot boards were turned toward one another as they passed, and the same conduct was in play when mounted riders or people on foot met. Many concepts are behind these applications (among which was the fact that most persons are right-handed and thus would want their dominant arm turned toward a potential challenger; consequently, turning the left side toward someone became regarded as an intentional affront or attempt to provoke), but the basic underlying reason was the belief that moving counterclockwise (or tuathal/widdershins) was harmful. When the American colonies rebelled against British rule, a number of customs and the like were intentionally changed (although by this time, the original bases of many of these customs was long forgotten by most), and one of those was the custom of driving on the left side of a road. Americans intentionally began driving on the right side of the road in order to distinguish themselves from the British. As a result of this change in driving wagons, carriages, carts, and so on, an American folkway is to walk on the right side of the sidewalk or hallway, whereas in Britain, the folkway continues to be walking on the left side of the pavement or hallway. Originally based on a variety of related religious and ethical concepts which were part of a worldview, these practices have now become, for most, semi-conscious traditional custom. When a member of one of these societies visits the other society and walks down the "wrong" side of the hallway or pavement/sidewalk, natives will feel uncomfortable, will regard the foreigner with some aversion, but some will not be entirely sure why they have these feelings, and even those who get the realization that the foreigner is walking on "the 'wrong' side," will still be extremely unlikely to question why that is "the 'wrong' side" or (in the case of Americans) how it came to be regarded as such (indeed, most will be unaware that it even became viewed as such, while instead subconsciously assuming that it has always been "the 'wrong' side").
In summary, then, an ethic is a static and more or less objective aspect of a worldview (cultural, philosophical, or religious), a morality is a relative aspect of a given society, scruples are individual and generally variable, and folkways are socio-cultural and relative but usually change only very slowly within a given society and/or culture.