The word 'tefillin' entered English directly from the post-biblical Hebrew təfillīn, which itself originates from the Aramaic plural form. Its core derives from the Hebrew noun tefillah (prayer), stemming from the root p-l-l, conveying the sense of "judgment" or "intercession." This etymological journey reflects the object's primary function as a physical instrument of prayer and devotion. The literal meaning, "prayers," evolved into the specific term for the phylacteries, which are understood in Jewish tradition not merely as symbols but as a means of binding oneself to God's commandments. Thus, the term encapsulates the concept of prayer made tangible through a ritual object.

The word is a loanword from Aramaic, adopted into Hebrew and subsequently into English. It is a plural form (singular: tefillah) derived from the Hebrew root p-l-l, meaning "to pray" or "to judge/intervene." The suffix -in is the Aramaic masculine plural absolute ending.