The adjective former means, broadly, earlier in time (during a former stage in the proceedings) or, of two things in succession, earlier in order (Our former manufacturing process was too costly). Erstwhile isn’t a viable synonym in these cases, but it does overlap in meaning with former in phrases like the former president, a former dancer, former members, her former husband, or my former home, where former refers to someone or something in terms of what they at one time were, but no longer are. Erstwhile has a literary ring to it; when former feels a bit too objective or emotionless or final, erstwhile is there to (potentially) soften your description of a role or relationship as no longer existing. This could be why some of the most common uses of this word are in the phrases erstwhile ally, friend, colleague, partner, and enemy, although you’re still far more likely to find former allies than erstwhile allies. Erstwhile’s use as an adjective (it was originally an adverb) has seen a slow but steady increase over the past century, and if that continues, it may eventually stake out clearer territory. It’s not over until it’s over.
When in the city, I sometimes run into one of my erstwhile Wall Street colleagues and enjoy the rush of gratitude I get afterwards for having chosen a different path.
We describe something as believable that is capable of being believed, or taken as true. A believable excuse is one that seems, or could be, true because, given everything we know and have experienced, the story told is in within the realm of possibility or probability. Believable is also applied to people (a believable witness), when their appearance, manner, and perhaps background lends credulity to what they say. Plausible is used primarily of things rather than people, and most frequently refers to the degree of truth or reasonableness in a claim or assertion. A plausible explanation or plausible scenario strikes the superficial judgment favorably, though it may or may not be true. The phrase plausible deniability is one that turns up especially in politics to talk about a scenario in which a denial of wrongdoing—or knowledge of wrongdoing—cannot be disproven.
Something that is messy is dirty, untidy, or disordered, for instance, a messy desk that is covered in papers and crumbs (we can relate!). When describing people or animals, messy usually refers to the cause of a mess, as a messy artist who leaves behind globs of glue and glitter. When the mess is centered on one’s appearance, disheveled may be more precise. While disheveled does not imply dirtiness like messy can, it does refer to something hanging loosely or in disorder, such as one’s clothes or hair, or to a general untidy or unkempt look. Someone who appears unshaven and with rumpled clothes can be described as looking disheveled. Although looking disheveled may indicate a lack of sleep, and is often associated with the adjectives disoriented and exhausted, it can also be used for a deliberate personal look: His disheveled appearance reflected his casual and cool style.