sweet-pea (n.)

Old English swete "pleasing to the senses, mind or feelings; having a pleasant disposition," from Proto-Germanic *swotja- (source also of Old Saxon swoti, Old Frisian swet, Swedish söt, Danish sød, Middle Dutch soete, Dutch zoet, Old High German swuozi, German süß), from PIE root *swād- "sweet, pleasant" (Sanskrit svadus "sweet;" Greek hedys "sweet, pleasant, agreeable," hedone "pleasure;" Latin suavis "pleasant" (not especially of taste), suadere "to advise," properly "to make something pleasant to"). Words for "sweet" in Indo-European languages typically are used for other sense as well and in general for "pleasing."

Then come kiss me, sweet-and-twenty!

Youth's a stuff will not endure.

["Twelfth Night"]

Also "being in a sound or wholesome state" (mid-13c.), and, of water, "fresh, not salt" (late Old English). As an intensifier from 1958. Sweet in bed (c. 1300) was the equivalent of modern "good in bed."

To be sweet on someone is recorded by 1690s. Sweet sixteen is recorded by 1767. Sweet dreams as a parting to one going to sleep is attested from 1897, short for sweet dreams to you, etc. Sweet-and-sour in cookery is from 1723 and not originally of Eastern dishes. Sweet nothings "sentimental trivialities" is from 1900. Sweet spot is from 1976, first in reference to tennis rackets. Sweet corn is from 1640s.

"the seed of a hardy leguminous vine," a well-known article of food, early or mid-17c., a false singular from Middle English pease (plural pesen), which was both single and collective (as wheat, corn) but the "s" sound was mistaken for the plural inflection. From Old English pise (West Saxon), piose (Mercian) "pea," from Late Latin pisa, variant of Latin pisum "pea," probably a loan-word from Greek pison "the pea," a word of unknown origin (Klein suggests it is from Thracian or Phrygian).

In Southern U.S. and the Caribbean, used of other legumes as well. Pea soup "soup made from peas" is recorded by 1711 (as pease-soup); the term was applied to London fogs at least since 1849. Pea-green as a hue resembling fresh peas is by 1752. Pea-shooter "toy consisting of a long straw or tube through which dried peas may be blown" is attested from 1803.