The Usual Semantic Trajectory
Words with multiple meanings typically have their concrete meanings before they develop their abstract ones: star referred to the thing in the sky before it referred to a brilliant performer. But sometimes a word's meaning moves in the other direction, as in the cases below.
Sloth
literal use : any of various slow-moving arboreal edentate mammals (genera Bradypus and Choloepus) that inhabit tropical forests of South and Central America, hang from the branches back downward, and feed on leaves, shoots, and fruits
original meaning : disinclination to action or labor : indolence
English had been making use of the word sloth for more than 400 years before speakers of the language decided in the early 17th century that a creature in South and Central America embodied the word. Sloth is from the Middle English word slouthe, itself from slow, meaning, er, "slow." (Incidentally, slow meant "stupid" before it described undercaffeinated people.)
Engine
literal use : a machine for converting any of various forms of energy into mechanical force and motion
original meaning 1 : ingenuity 2 : evil contrivance : wile
The word engine may today mostly evoke the thing under a car's hood, but the word existed long before the Model T. Originally from the Latin ingenium, meaning "natural disposition, talent," engine has over its 700-year existence had a number of meanings not yet touched upon here, including "torture implement" and "computer software that performs a fundamental function especially of a larger program."
Jactitation
literal use : a tossing to and fro or jerking and twitching of the body
original meaning : boastful public assertion or ostentation
Jactitation is most often encountered in medical contexts, where it's used especially to refer to the excessive restlessness suffered in particular psychiatric disorders. This technical medical use—which ties nicely to the word's Latin root jactare, meaning "to throw"—makes its earlier meanings somewhat surprising: it entered the language as a term for ostentation or the act of boasting in public, and went on to develop application in referring to the act of falsely claiming to be married to someone, or to having a particular title.
Parasite
literal use : an organism living in, with, or on another organism in an intimate association in which it obtains benefits from the host organism which it usually injures
original meaning : a person who exploits the hospitality of the rich and earns welcome by flattery
The human parasite is the original parasite. The word, which is ultimately Greek, from para- and sitos, meaning "grain, food," even featured as the name of a stock character in Greek and Roman comedy: Parasite was the guy who gets the wealthy and influential character to give him food by tending to the host's ego, love life, and attention span.
Dilate
literal use 1 : to enlarge or expand in bulk or extent 2 : to become wide
original meaning : to describe or set forth at length or in detail
Although the Latin source of dilate, dilatere, means literally "to spread wide," the earliest known instances of the word in English set it squarely in contexts relating to discourse. To dilate something, originally, was to describe it at length or in detail. While listening to someone dilate, say, their fancy dinner out sounds painful, we're betting that anyone who's ever been in labor would prefer that dilation to the kind better known today.
Gravity
literal use : the natural force that tends to cause physical things to move towards each other : the force that causes things to fall towards the Earth
original meaning : dignity or sobriety of bearing
More than 150 years before the apocryphal apple plunked down upon Isaac Newton's head, gravity was a word that referred to the way we might imagine the father of modern science (as Newton is sometimes called) to carry himself. The word's source is Latin gravis, meaning "heavy." Over the years gravity has also referred to such things as importance, seriousness, and weight.