What is the suffix of roughshod?

Answer 1

The word, "roughshod", is a compound word, comprised of two distinct words, rough and shod. As such, it contains neither suffix nor prefix.
An example of a prefix is found in the word "prehistoric", where "pre" (meaning before) is the prefix. The prefix here qualifies the following word, so we understand prehistoric to mean before history.
An example of a suffix is found in the word "loudly", where "ly" is the suffix. The ly is not a word unto itself, but rather changes the base word, loud, from an adjective into an adverb, so we say, "The teacher had to speak very loudlyto be heard over the confusion."

Answer 2

The suffix of "roughshod" is "-shod." In this case, "shod" is a past participle form of the verb "shoe." "Roughshod" means to ride horses without shoes, often to indicate a harsh or ruthless manner.