Enthusiastic and avid both refer to having or showing an energetic interest in something or an eager willingness. Enthusiastic, the more common word, has a wider range of application than avid. It implies spirited interest, motivation, or approval, and often involves an outward demonstration of these states (an enthusiastic reaction). Avid suggests a sort of hungry eagerness and sustained or committed interest, usually in the pursuit of an activity, especially a hobby (an avid reader, an avid snowboarder, an avid fan). Avid describes a quality of the pursuit, as much as or more than the state or attitude of a person—we don’t say someone is avid about snowboarding. However, in a much less common sense of avid, people can be said to be avid for, that is, eagerly desirous of, something anticipated (readers avid for the author’s next book).
Stubborn and obstinate imply resistance to advice, objection, pleading, or force. Both words are frequently found paired with refusal and resistance (obstinate resistance to change), and stubborn people can be as frustratingly unyielding as obstinate people. At the same time, the word stubborn might convey admirable qualities such as perseverance and determination, whereas obstinate can carry more negative connotations of a harmful rigidity, arrogance, or perversity. The obstinate are more likely to dig in their heels on the wrong side of an issue (obstinate refusal to admit his error). Typical adverbs used to characterize obstinate include incorrigibly and arrogantly.
A resident is someone who lives in a specified place (a resident of Oklahoma, an apartment that accommodates three residents). Outside of legal and other official contexts, denizen is a strong synonym for resident (a denizen of Jersey City), but its range of reference stretches to non-human inhabitants (denizens of the deep, a denizen of planet Zork) and places that are not ordinarily considered residences (internet denizens, a denizen of the underworld (mythical or criminal)). Another definition of denizen is a person who regularly frequents or hangs out at a place (denizens of the local bar), and it’s not always clear, in phrases like “denizen of the lunatic fringe,” which of these definitions is intended. The common thread is that denizens either live or are very much at home in these “places.”