Old English: an irregular verb whose full conjugation derives from several originally distinct verbs.
http://www.askoxford.com/concise_oed/bexx?view=uk
Word History
The prehistoric Germanic word from which be is derived, is also the ancestor of English boor, booth, build, husband, and neighbor, and perhaps also of bylaw.
http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861589419
Originated before 900 from Middle English been < Old English beon, from beo + -n, infinitive suffix. Irregular forms inherited from the Old English compound verb bēon-wesan.
http://en.wiktionary.org/wiki/be
Origin:
bef. 900; ME been, OE bēon (bēo- (akin to OFris, OHG bim, G bin, OS bium, biom (I) am, OE, OHG, OS būan, ON būa reside, L fuī (I) have been, Gk phy- grow, become, OIr boí (he) was, Skt bhávati (he) becomes, is, Lith búti to be, OCS byti, Pers būd was)) + -n inf.
http://dictionary.reference.com/search?q=be&r=66
O.E. beon, beom, bion “be, exist, come to be, become,” from P.Gmc. *beo-, *beu-. Roger Lass (“Old English”) describes the verb as “a collection of semantically related paradigm fragments,” while Weekley calls it “an accidental conglomeration from the different Old English dial[ect]s.” It is the most irregular verb in Mod.E. and the most common. Collective in all Gmc. languages, it has eight different forms in Mod.E.: BE (infinitive, subjunctive, imperative), AM (present 1st person singular), ARE (present 2nd person singular and all plural), IS (present 3rd person singular), WAS (past 1st and 3rd persons singular), WERE (past 2nd person singular, all plural; subjunctive), BEING (progressive & present participle; gerund), BEEN (perfect participle). The modern verb represents the merger of two once-distinct verbs, the “b-root” represented by be and the am/was verb, which was itself a conglomerate. The “b-root” is from PIE base *bheu-, *bhu- “grow, come into being, become,” and in addition to Eng. it yielded Ger. present first and second person sing. (bin, bist, from O.H.G. bim “I am,” bist “thou art”), L. perf. tenses of esse (fui “I was,” etc.), O.C.S. byti “be,” Gk. phu- “become,” O.Ir. bi’u “I am,” Lith. bu’ti “to be,” Rus. byt’ “to be,” etc. It is also behind Skt. bhavah “becoming,” bhavati “becomes, happens,” bhumih “earth, world.”
http://www.etymonline.com/index.php?term=be
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Idioms