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:
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?