Using enumitem, how can I remove the label and the indent from an individual item in a list?

Question

I am creating a list in LaTeX using the enumitem package, and having trouble setting the alignment of one item in the list. For that one item, I want to remove the label and decrease the indent so that item is aligned with the labels of the previous items.

Here is the code I am currently using:

\usepackage{enumitem}

\begin{enumerate}
  \item Item 1
  \item Item 2
  \item Item 3
  \item Item 4
  \item[] Item 5
\end{enumerate}

Which looks like this:

1. Item 1
2. Item 2
3. Item 3
4. Item 4
   Item 5

But what I want is this:

1. Item 1
2. Item 2
3. Item 3
4. Item 4
Item 5

Making a new paragraph doesn't work because LaTeX automatically creates space after the list and Item 5 needs to be part of the list.

Thanks in advance!

Answer 1

Changing your syntax slightly (just to add more functionality), you can use \item*:

\documentclass{article}

\usepackage{enumitem,xparse}

\setlength{\parindent}{0pt}% Just for this example

\let\oldenumerate\enumerate
\let\endoldenumerate\endenumerate
\RenewDocumentEnvironment{enumerate}{O{}}
  {\begin{oldenumerate}[#1]
     \let\olditem\item
     \RenewDocumentCommand{\item}{s}{%
       \IfBooleanTF{##1}
         {\olditem[]\hspace*{\dimexpr-\labelindent-\labelwidth-\labelsep}\ignorespaces}
         {\olditem}}
     }
  {\end{oldenumerate}}

\begin{document}

Some reference text.

\begin{enumerate}
  \item Item 1
  \item Item 2
  \item Item 3
  \item Item 4
  \item[] Item 5
\end{enumerate}

Some reference text.

\begin{enumerate}[label=\roman*]
  \item Item 1
  \item Item 2
  \item Item 3
  \item Item 4
  \item* Item 5
\end{enumerate}

Some reference text.

\end{document}

The above redefinition of the enumerate environment keeps the optional argument functionality provided by enumitem while changing the way \item functions; it adds a starred \item* version. This *-version sets a regular \item[] and backspaces to the margin.