Merely means "only." If you say "I was merely trying to help," your efforts were probably not appreciated and you're likely to be stalking off with your nose in the air. Merely comes from the Latin merus, ("undiluted"). But "undiluted" is positive — as in, "that's the undiluted truth" — in a way that merely is not.

What does merely mean?

: nothing more than : only was merely trying to help …

Does merely mean simply?

only as specified and nothing more; simply: merely a matter of form.