Etymology
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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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scream (n.)

c. 1500, "a sharp, piercing sound or cry," expressive of pain, alarm, etc., from scream (v.).

And (as they say) lamentings heard i' th' Ayre; Strange Schreemes of Death. ["Macbeth," II.iii.61]

That spelling probably reflects "sk-" as spelled in words from Latin (such as school; see sch); his early editions also have schreene for screen. The slang meaning "something very great, excellent, or exciting," especially "something that evokes a cry of laughter" is by 1888; screamer in this sense is from 1831.

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