Why is 'shucks' (as in 'aw, shucks') used with an '-s' ending?

Question

I understand that 'shucks' is a slang that is:

used especially to express mild disappointment or embarrassment

and this definition is listed separately from 'shuck' (the verb/noun) in merriam-webster.

Oxford dictionary online lists 'shucks' under 'shuck' as:

exclamation

(shucks) informal

used to express surprise, regret, irritation, or, in response to praise, self-deprecation: 'Thank you for getting it.' 'Oh, shucks, it was nothing.'

But neither explains why the exclamation must be 'shuck' + 's'. I don't really know if the 's' expresses a plural (from the noun 'shuck') or a 3rd person singular (from the verb 'shuck').

Some online sources like Urban Dictionary says it is

a combination of f*** and sh*t

which I'm not really believing as I don't really hear people say 'aw f**k sh*ts' -it'd be more like 'f***ing sh*t'.

So, why is there an '-s' ending in this usage?

Answer 1

Etymonline lists the origin of shucks thusly:

Interjection shucks is 1847, from sense of "something valueless" (not worth shucks).

So, the -s termination comes from the plural in the original, longer expression.