What is the meaning behind the word Tefillin?
The word Tefillin comes from the word Pelila/Testimony, as the Tefillin are a testimony that the Divine presence dwells upon us. Alternatively, the term Tefillin comes from the word Haflah which means unique, as the Jewish people are unique from amongst the nations.
 Tur 25
 Beis David 20; Ashel Avraham Openheimer