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.
Here's the scoop on today's pair of words: the very general verb dig refers literally to the breaking up or turning over of earth or sand, as with a shovel, spade, or bulldozer. Figuratively, it’s used to talk about finding or discovering something by effort or search: a gossip columnist might dig up some dirt (scandalous information) on a celebrity. The synonym delve has a narrower range of applications; it is most commonly used to refer to examining something carefully: the article delved into the issue of prison reform. Sometimes delve suggests sustained intensive research, more along the lines of the verb investigate. While the distinction seems clear enough today, when delve entered English (long before dig, mind you) it referred to digging up the earth in preparation for planting. Dig overtook delve as the go-to verb for such terrestrial matters, and nowadays the only shoveling delve does is through piles of information.