It is clearly input. But why?
I can put something, which is to say that I can place it, or give it, or present it.
Why? Put is a verb. Only.
- I put the crown onto the frog. The crown however is not the “put”, it’s simply the crown.
I can however input something – type it in, place it in, draw it in – and I can also have input.
Input is a verb and a noun.
- I input my blog into the inter-webs. Or. The inter-webs input is my blog. (note: no apostrophe s (‘s) on interwebs as it’s not possessive)
The “in” is not a prefix!
If it was a prefix it would change the meaning of put to mean “not” put, as that is what the prefix “in” does.
incapable, not capable
incapacitated, without capacity
inconceivable, not conceivable
input, not put. Is wrong, as input is absolutely guaranteed to be put.
We get a better sense of how it’s come about from its antonym output, being stuff that’s come out.
Both of these words are, of course, compound words the joining of two words to create a new meaning.
Other examples include: backyard, courthouse, anywhere, thunderstorm, cupcake and, of course, interwebs.
Imput then is clearly not a word, even though you see it everywhere.
Putt putt is a kind of golf where you putt only. The object is to putt it only once each turn.
In-putt-putt is not a word form (neither is inputtputt, inputt, or ingolf).