Yes, there are some words that are not available; but this is actually not a restriction of Contact Form 7, but a restriction of WordPress.

If you post an input field with a name that is the same as a parameter name already used in a WordPress query, WordPress will confuse them, so you can’t use that name.

The followings are parameter names that WordPress uses in a query: m, p, posts, w, cat, withcomments, withoutcomments, s, search, exact, sentence, calendar, page, paged, more, tb, pb, author, order, orderby, year, monthnum, day, hour, minute, second, name, category_name, tag, feed, author_name, static, pagename, page_id, error, attachment, attachment_id, subpost, subpost_id, preview, robots, taxonomy, term, cpage, post_type, and embed.

For example, ‘name’ is used in the query, so ‘name’ is not available for a field name. The best practice in avoiding unavailable names is adding a prefix or suffix to the name, for example, use ‘your-name’ or ‘name-1234’ instead of ‘name’.

See also: My contact form always redirects to 404 error page after submission.