FAST
Prologue
The most important English word related to the holy month RAMADAN is the word "fast". We say; "we fast", "we are fasting", "she doesn't fast, when she is so", "most children like to pretend to fast", etc.
But remember that the word "fast" is a multi-class English word. It means that it can be either a noun, an adjective, a verb, or an adverb. Each one of its four classes has been defined in the first volume of The New Shorter Oxford English Dictionary, page 920. Only, when it is a verb or a noun it can be related to the holy Ramadan.
"Fast" as a verb
Meaning
In the case "fast" is a verb, it means "to eat no food for a period of time". MWD defines it as:
1 : to abstain from food,
or
2 : to eat sparingly or abstain from some foods.
Etymology
Dictionary.com explains its etymology as following: "fast O.E. fæstan "to fast" (as a religious duty), from P.Gmc. *fastejan (cf. O.Fris. festia, O.H.G. fasten, O.N. fasta), from the same root as fast (adj.). The original meaning was "hold firmly," and the sense evolution is via "firm control of oneself," to "holding to observance" (cf. Goth. fastan "to keep, observe," also "to fast"). Presumably the whole group is a Gmc. translation of M.L. observare "to fast." Related: Fasted; fasting."
Explanation of the etymology
This etymology explains that the word "fast" comes from the Old English word "fæstan" which means "to fast" (as a religious duty).
Then the word "fæstan" comes from Proto-Germanic (language) word *fastejan.
In terms of its origin, the word "fæstan" is the same as the Old Frisian language word "festia", Old High German word "fasten", Old Norse "fasta", from the same root as "fast" (adj.). The New Shorter Oxford Dictionary also equalises them; as it writes: "fast /fɑːst/ v. [OE fæstan = OFris. festia, (M)Du. vasten, OHG fastēn, (G fasten), ON fasta, Goth. fastan, f. Gmc.]". (V:1. P:920)
The original meaning was "hold firmly," and the sense evolution is via "firm control of oneself," to "holding to observance" ( = when someone obeys a law or does something because it is part of a religion, custom, or ceremony
observance). It is the same as the Gothic word "fastan" which means "to keep, observe," also "to fast".
Finally it says; presumably the whole group is a Germanic translation of Medieval Latin "observare" meaning "to fast."