Rain [ren (Saxon), of renian (Saxon) prob. of ααεβ (Greek) a drop of ααἱνι (Greek) to drop Regn (Su. and Du.)]
a vapour drawn by the sun, and falling to the earth in drops.
Rain is formed of the particles of vapours, joining together, which, being joined, fall down to earth. The difference between Dew and Rain seems chiefly to be this, that Dew falls at some particular times, and in very small drops, so as to be seen, when it is down, but is scarce perceivable while falling; whereas Rain is grosser, and falls at any time.
There are several causes, that may singly, or jointly, produce Rain.
1. The coldness of the air may make the particles of the clouds to lose their motion, and become less able to resist the gravity of the incumbent Air, and of consequence to yield to its pressure, and fall to the ground.
2. The vapours may be gathered by the wind in such abundance, as first to form very thick clouds, and then squeeze those clouds together, till the watery particles make drops too big to hang any longer in the Air.
3. When the vapours arise in so great abundance, as to reach and mingle with the clouds above them, then they cause Rain in very large drops; and this may happen in still sultry weather, because then the Clouds having no sensible motion, and in the mean time the Heat filling the Air with vapours, they joining with the clouds, and being stopp’d in their progress, do open a passage for the stores of the clouds to descend upon the earth,
4. Sometimes the warm wind thaws the frozen clouds into drops, as we see snow dissolved by heat. Now the thicker and sooner any such cloud was gathered, the larger the drops will be, because there was greater store of vapours condensed there. And hence it is, that in summer time, we have sudden showers of rain in exceeding great drops. See Snow and Hail.

Definition taken from The Universal Etymological English Dictionary, edited by Nathan Bailey (1736)

Rackooˊn * Rates of Ships
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Rates of Ships
Rectaˊngular [with Geom.]
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Reˊscous in Law
Reˊsident [ant. Customs]
Reveˊrsed [in Herald.]