Old English wesan, wæs, wæron 1st and 3rd person singular of wesan "to remain," from Proto-Germanic *wesanan (source also of Old Saxon wesan, Old Norse vesa, Old Frisian wesa, Middle Dutch wesen, Dutch wezen, Old High German wesen "being, existence," Gothic wisan "to be"), from PIE root *wes- (3) "remain, abide, live, dwell" (cognates Sanskrit vasati "he dwells, stays;" compare vestal). Wesan was a distinct verb in Old English, but it came to supply the past tense of am. This probably began to develop in Proto-Germanic, because it is also the case in Gothic and Old Norse. See be.
A similar formation appears in Old English wes þu hal, but this is not recorded as a drinking salutation. Sense extended c. 1300 to "liquor in which healths were drunk," especially spiced ale used in Christmas Eve celebrations. Meaning "a carousal, reveling" first attested c. 1600. Wassailing "custom of going caroling house to house at Christmas time" is recorded from 1742.
In Old English it formed only present tenses, all other forms being expressed in the W-BASE (see were, was). This cooperative verb is sometimes referred to by linguists as *es-*wes-. Until the distinction broke down 13c., *es-*wes- tended to express "existence," with beon meaning something closer to "come to be."
Old English am had two plural forms: 1. sind/sindon, sie and 2. earon/aron. The s- form (also used in the subjunctive) fell from English in the early 13c. (though its cousin continues in German sind, the 3rd person plural of "to be") and was replaced by forms of be, but aron (see are) continued, and as am and be merged it encroached on some uses that previously had belonged to be. By the early 1500s it had established its place in standard English.
Old English beon, beom, bion "be, exist, come to be, become, happen," from Proto-Germanic *biju- "I am, I will be." This "b-root" is from PIE root *bheue- "to be, exist, grow," and in addition to the words in English it yielded German present first and second person singular (bin, bist, from Old High German bim "I am," bist "thou art"), Latin perfective tenses of esse (fui "I was," etc.), Old Church Slavonic byti "be," Greek phu- "become," Old Irish bi'u "I am," Lithuanian būti "to be," Russian byt' "to be," etc.
The modern verb to be in its entirety represents the merger of two once-distinct verbs, the "b-root" represented by be and the am/was verb, which was itself a conglomerate. 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 Modern English and the most common. Collective in all Germanic languages, it has eight different forms in Modern English:
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 paradigm in Old English was: eom, beo (present 1st person singular); eart, bist (present 2nd person singular); is, bið (present 3rd person singular); sind, sindon, beoð (present plural in all persons); wæs (past 1st and 3rd person singular); wære (past 2nd person singular); wæron (past plural in all persons); wære (singular subjunctive preterit); wæren (plural subjunctive preterit).
The "b-root" had no past tense in Old English, but often served as future tense of am/was. In 13c. it took the place of the infinitive, participle and imperative forms of am/was. Later its plural forms (we beth, ye ben, they be) became standard in Middle English and it made inroads into the singular (I be, thou beest, he beth), but forms of are claimed this turf in the 1500s and replaced be in the plural. For the origin and evolution of the am/was branches of this tangle, see am and was.
That but this blow Might be the be all, and the end all. ["Macbeth" I.vii.5]
1690s, "feeble or poor in quality," reduplication of washy "thin, watery." Meaning "vacillating" is attested by 1873.
also kirschwasser, "liquor distilled from fermented cherry juice," 1778, from German Kirschwasser, literally "cherry-water;" first element from Middle High German kirse, from Old High German kirsa, from Vulgar Latin *ceresia, from Late Latin cerasium "cherry" (see cherry). For second element, see water (n.1).