Etymology
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inertia (n.)
1713, "that property of matter by virtue of which it retains its state of rest or of uniform rectilinear motion so long as no foreign cause changes that state" [Century Dictionary], introduced as a term in physics 17c. by German astronomer and physician Johann Kepler (1571-1630) as a special sense of Latin inertia "unskillfulness, ignorance; inactivity, idleness," from iners (genitive inertis) "unskilled; inactive" (see inert). Also sometimes vis inertia "force of inertia." Used in 1687 by Newton, writing in Modern Latin. The classical Latin sense of "apathy, passiveness, inactivity" is attested in English from 1822.
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inertial (adj.)
"pertaining to inertia," 1737, from inertia + -al (1). Related: Inertially.
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*ar- 
also arə-, Proto-Indo-European root meaning "to fit together."

It forms all or part of: adorn; alarm; aristarchy; aristo-; aristocracy; arm (n.1) "upper limb of the body;" arm (n.2) "weapon;" armada; armadillo; armament; armature; armilla; armistice; armoire; armor; armory; army; art (n.) "skill as a result of learning or practice;" arthralgia; arthritis; arthro-; arthropod; arthroscopy; article; articulate; artifact; artifice; artisan; artist; coordination; disarm; gendarme; harmony; inert; inertia; inordinate; ordain; order; ordinal; ordinance; ordinary; ordinate; ordnance; ornament; ornate; primordial; subordinate; suborn.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit irmah "arm," rtih "manner, mode;" Armenian arnam "make," armukn "elbow;" Greek arti "just," artios "complete, suitable," artizein "to prepare," arthron "a joint;" Latin ars (stem art-) "art, skill, craft," armus "shoulder," artus "joint," arma "weapons;" Old Prussian irmo "arm;" German art "manner, mode."
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Laocoon 

also Laocoön name of a Trojan priest of Apollo, from Latin Laocoon, from Greek Laukoun, from laos "people" (see lay (adj.)) + koeo "I mark, perceive."

Laocoön, n. A famous piece of antique sculpture representing a priest of that time and his two sons in the folds of two enormous serpents. The skill and diligence with which the old man and lads support the serpents and keep them up in their work have been justly regarded as one of the noblest artistic illustrations of the mastery of human intelligence over brute inertia. [Ambrose Bierce, "Devil's Dictionary," 1911]
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