See various definitions here:
Built-in (adj): included as part of something and not separate from it.
In-built (adj) is used less frequent: Meaning is the same as above. (So, both can be used to describe that Siri is an in-built/a built-in feature of an iPhone. BUT… then it says compare…Inbuilt (adj): an inbuilt quality exists as an essential part of something/somebody. BUT…then…
Built-in = In-built (adj.): integral. On the other hand Builtin returns no results on Oxford but redirects to in-built. Isn't it a word if inbuilt is?
Is saying "Siri is an inbuilt feature of an iPhone since its inception" correct? Inbuilt php functions is quite common phrase used in technology. Is it its natural functionality? Is it correct to use builtin anywhere?
Best Answer
I am a native English speaker and I would use "built-in" almost exclusively for all definitions you provided although I would recognize "inbuilt" as having an identical meaning. I've heard some people use "built-in" to indicate that a feature was added (after-the-fact) in a way that is permanent and integrated with the whole unit.
An example would be, I added built-in bookshelves to my living room. It means that they were built into the house, attached to the structure, and cannot be relocated or removed without some demolition. An example of inbuilt would be the programming example you gave where the feature was there from the start, designed into the language, and an integral part of it.
I think they are completely interchangeable.