In Bikes, major part plays by 4 stroke petrol engine, then why did they named as motor bike or cycle instead of engine bike?
An internal combustion engine is a motor in the literal sense
Consider the following examples:
A rotor is an object that undergoes rotation via an external energy source.
Examples of rotors include brake discs and the vanes in a turbocharger
A stator is an object that remains fixed in its relative position (station-ary) that often complements a rotor.
In car applications, the stationary part of a torque converter is a good example of this.
A motor enables motion of other components
For example, electrical motors are used to rotate the vanes in most residential water pumps.
Similarly, an engine provides motive force to turn the wheels of a vehicle. From this perspective, an engine is an example of a motor; it enables motion.
Most of the world uses the word motor for what engine is in current English (although note that engine also has different meanings, for instance, locomotive). This means that although engine is what you normally use to describe what's under your hood or bonnet, compound words that entered English as already combined notions (like motorcycle) usually arrived with the more international root motor-.
But this doesn't only apply to these coumpound words. English has a great deal of its own words that start with it: motorway (the British version of highway), motorhome, motor trade, motor sports and motor vehicle (see the title of the site we're currently on).
So, simply accept that, even though engine and motor are somewhat separated in meaning and usage in today's English (not to mention the differences between, say, American and British usage), they have basically and fundamentally the same meaning: a device to transform some other form of energy into mechanical energy.
According to Etymology.com:
motorcycle (n.) Look up motorcycle at Dictionary.com 1895, a hybrid from motor + -cycle, from bicycle. Motocycle also was used late 19c.
The horse follows the crooks of a country road, but then the training of the "motorcycle" (horrid name) will inevitably straighten out the crooks in the country road, and afford long ranges of straight tracks. [Payson Burleigh, "The Age of Steel," Oct. 12, 1895]
That gives the story of how the name came about: the hybrid addition of motor to cycle. I don't believe that is your real issues though, correct? You are wondering why the use of the word motor as opposed to using engine.
I believe this comes from the belief that the words engine and motor are not (for the most part) interchangeable. Motor must refer to an electric motor and engine must refer to an internal combustion engine. This very much so is a fallacy.
Dictionary.com has as it's first and second entries for motor as:
- a comparatively small and powerful engine, especially an internal-combustion engine in an automobile, motorboat, or the like. [emphasis mine]
- any self-powered vehicle.
An automobile can be called a motor vehicle. It isn't named an engine vehicle. The truth is, the words motor and engine are fairly much interchangeable in the English vernacular of today. It's just one of those quirks which has slated the name for the motorcycle.
The specific, historically recent meanings we have are these:
'motor' - made of wires and magnets and a core, an electric moving-thing
'engine' - made of an engine block with pistons and a cam shaft etc, running on liquid fuel
But 'motor' has the same root as 'move' from ancient times, before electricity was discovered. For example 'motor cells' in biology aren't electrical, but they are cells like muscle cells that have the ability to move the parts of a biological organism. And 'fine motor control' can refer to the human ability to drop pins into tiny holes rapidly on an assembly line, for example.
I think that older sense of 'motor' was being applied when the term 'motor-cycle' was invented. I think that is the basic reason although I'm sure some real etymologists out there could improve my answer significantly. Also if you look for 'motor etymology' or 'engine etymology' on a search engine I am sure you will find a lot!
I believe you'll find that "engine" isn't used to modify another noun except self-referentially. It can be used self-referentially, as in "engine speed" (where the idea could be phrased "speed of the engine"), but not otherwise.
"Engine [bi]cycle" can't be rephrased as "[bi]cycle of the engine", so it would sound odd to hear, or read, "enginecycle". Someone hearing/reading that would think it meant "operating cycle (e.g. 2-stroke, 4-stroke) of the engine", so it would take awhile to sort out the confusion.
According to http://www.oxforddictionaries.com/definition/english/engine "engine" can only be a noun. The adjective is "engined," (as in "a twin-engined aircraft") but nobody uses the term "an engined bike".
On the other hand "motor" can be an adjective as well as a noun: http://www.oxforddictionaries.com/definition/english/motor. Hence "motor bike". The longer adjective "motorized" is used to describe some devices, but not bikes.
Languages are not logical. English is just what it is.
The word "engine" has the same root as "ingenious". Historically it meant "ingenious machines" which were not "engines" in the modern sense.