What word can "-sies/-ies" be added?
I often hear words that end with -sies or -ies in informal conversation like:
- No backsies.
- Let's go halfies.

Can it the same way they do with "thingy"? ( y, ie) ? Or are they fixed slangs?

How do I know what word I can add the -ie/-ies (or -y if that's the same category)?

Question

What word can "-sies/-ies" be added?
I often hear words that end with -sies or -ies in informal conversation like:
- No backsies. 
- Let's go halfies.

Can it the same way they do with "thingy"? ( y, ie) ? Or are they fixed slangs?

How do I know what word I can add the -ie/-ies (or -y if that's the same category)?

Answer

it should be half-sies
or halfy halfy = to share in half
or halfsie halfsie to share half and half.

basically it's just an informal often childlike way of speaking where the child puts on an 'es' or 'ies' onto words that do not usually require them; children are still developing listening and grammar skills.

A few [very few] of these children trying to speak words have come to be used in general conversation. You should not dwell on trying the learn the very few that may exist.

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