\documentclass{article}
\usepackage[all]{xy}
\usepackage{amsmath,xcolor}
\newcommand{\lambdabar}{{\mkern0.75mu\mathchar '26\mkern -9.75mu\lambda}}
%\newcommand{\Tbar}{{\mkern0.75mu\mathchar '26\mkern -9.75mu T}}
\newcommand{\Tbar}{\raisebox{0.2ex}{--}\kern-0.6em T}
\begin{document}
\noindent
\pagestyle{empty}
\huge
\[
	\xymatrix@C=0.5em@R+1em{
	& \underset{_{\substack{\text{linear}\\\text{wavenumber}}}}{\tilde{\nu}}
	\ar^-{_{\cdot 2\pi}}[rr]
	\ar^>>>>>>>>>>>>>>>>>>>>{()^{-1}}@{<.>}[dd]
	\ar_-{_{\cdot c}}[dl]
	&
	& \underset{_{\substack{\text{angular}\\\text{wavenumber}}}}{k}
	\ar^-{_{\cdot c}}[dl]
	\ar^-{()^{-1}}@{<->}[dd]
	\\
	\underset{_{\substack{\text{linear}\\\text{frequency}}}}{f}
	\ar^{_{\qquad\;\; \cdot 2\pi}}[rr]
	&
	& \underset{_{\substack{\text{angular}\\\text{frequency}}}}{\omega}
	\ar^>>>>>>>>>>>>>>>>>>>>{()^{-1}}@{<->}[dd]
	\\
	& \underset{_{\substack{\text{linear}\\\text{wavelength}}}}{\lambda}
	\ar^-{_{\qquad\quad\cdot \frac{1}{2\pi}}}@{.>}[rr]
	\ar^>>>>>>>>>>>>>>>{_{\cdot \frac{1}{c}}}@{.>}[dl]
	&
	& \underset{_{\substack{\text{angular}\\\text{wavelength}}}}{\lambdabar}
	\ar^-{_{\cdot \frac{1}{c}}}[dl]
	\\
	\underset{_{\substack{\text{linear}\\\text{period}}}}{T}
	\ar^-{()^{-1}}@{<->}[uu]
	\ar^-{_{\cdot \frac{1}{2\pi}}}[rr]
	&
	& \underset{_{\substack{\text{angular}\\\text{period}}}}{\Tbar}
	}
\]

\vspace{1em}
\Large

\noindent
$c =$ speed of wave propagation (phase velocity), from the Latin word "celeritas" (speed or swiftness).\\
%%%$x =$ generalized variable name\\

\end{document}