Curious to understanding a word formation

Question

I am currently studying English language acquisition and an early elementary grade leveled subject's assessment results. The subject was asked to repeat a series of complex sentences. One of the sentences read:

My friend likes to eat ice cream when it's very hot out.

The subject responded:

My friend likes to eat ice cream when it's really hot outside.

I'm curious to know which type of morpholocical word formation would changing the word out to outside fall under? Derivational or compounding?

Also, what about replacing the word very with really even though they both never change their grammatical category? Would this be a simple substitution?

Any input would be appreciated. Thanks

Answer 1

I don't see why morphological formation is relevant. Just as with very and really, the subject has substituted another word of similar meaning: it just happens that outside contains the same morpheme as out.

[I don't know whether or not it is relevant that out in this sense is rather restricted in its use: it can follow a verb of being, going or putting (when I was out, I'm going out), or an adjective of weather (it's cold out, it was wet out) but not very much else. So the subject has substituted a possibly problematic word by a more straightforward one.]