If we assume this is what the OP meant,
That is what should have been done. Despite the poor syntax, we have
Can someone tell me where this word comes from?
I can’t see that there is much that is unclear about that.
It is not a matter of whether or not the OP comes back – EL&U is creating a reference source, so, for what it’s worth:
The word starts in English as a rush of water and/or the channel that contains it.
The use of “race” is then split into the several attributes of speed and power, and a channel or pathway:
Etymology: < early Scandinavian (compare Old Icelandic rás , Norwegian regional rås , Swedish regional rås running, rush (of water), course, channel, way), cognate with rese n.
I. With reference to a person, animal, etc.: forward progression, running, or movement; an instance of this.
†1. A rush, onset, charge; a raid. Obsolete.
c1330 (▸?a1300) Arthour & Merlin (Auch.) (1973) 3990 (MED) Wiþ gret ras King Ban þai hitten alle at ones. [King Ban rushed them all at once.]
And about the same time:
II. A path, channel, or course, and related senses.
5.†a. The course, line, or path taken by a person or a moving body. Also figurative. Obsolete.
c1390 (▸c1300) MS Vernon Homilies in Archiv f. das Studium der Neueren Sprachen (1877) 57 274 (MED) To toune I renne þe deueles ras. [To town, I ran along the Devil's path]
There then developed the idea of a figurative sense of a narrow path:
†4.a. figurative or in figurative context: a person's progress through life or some part of it. Obsolete. The metaphor of life as a [competative] race is now more commonly understood as the figurative use.
a1450 (▸c1412) T. Hoccleve De Regimine Principum (Harl. 4866) (1897) 1448 (MED) I whilom þoghte Han ben a prest; now past am I þe raas. [I had thought for a while that He was a priest, I am now persuaded [that He is] the pathway (through/of) life]
As water-power became more popular:
>5.b. A channel or bed (of a stream); spec. an artificial channel leading water to or from a point where its energy is utilized, as in a mill or a mining claim. head-, mill-, tail-race: [etc.]
1570 in J. Raine Depositions Courts Durham (1845) 212 The [law-] suit..for the raic [e] of the said water corne myln. [The [law suit..for the race of the said water-powered corn mill.]
The change from a straight or direct pathway/channel to a circular one did not arise until quite late:
OED at "wheel"
wheel-race n. the part of a mill-race in which the mill-wheel is fixed.
1825 ‘J. Nicholson’ Operative Mechanic 104 The wheel-race should always be built in a substantial manner with masonry.
And then, with the invention of ball- and roller-bearings:
8.c. Mechanics. Either of the two grooved rings between which run the balls of a ball bearing or the rollers of a roller bearing. Recorded earliest in ball race (see ball n.1 Compounds 2), roller race (see roller n.1 Compounds 5).
1896 Bangor (Maine) Daily Whig & Courier 13 Nov. 4/4 One of the novelties that will be sure to attract attention at the coming bicycle shows is an ingenious arrangement for conducting oil to the ball race.
Thus we can see that, in the sense of head-race, "Head" = highest; most important (Cf "headmaster") and the word "race" has returned to (or never left) its origins of being "a constraining channel through which something rushes", i.e. the bearings.