Another name for the pilgrimage festivals is regalim רגלים , or in the singular רגל regel. While this meaning is used extensively in rabbinic literature, it appears only once in the Tanach, and had a different connotation. As Klein writes:
The literal meaning of שלש רגלים is 'three feet, three steps', whence arose the meaning 'three times'. From שלש רגלים in the verse Exodus 23:14 שָׁלֹשׁ רְגָלִים, תָּחֹג לִי בַּשָּׁנָה ('Three times you shall keep a feast unto me in the year') developed in post-Biblical times the meaning of שלש רגלים as 'the three festivals of pilgrimage' (first used in this sense in the Mishnah), whence - through back formation - the singular רגל was also used in the sense of festival of pilgrimage.
While there are examples in the Rabbinic literature which connect the concept of regel as pilgrimage and the more basic meaning of regel as foot (see the first mishna in Chagiga), it is clear from the story of Bilaam that regel could mean "(a) time" without direct connection to feet. There, Bilaam's donkey asks "What have I done to you that you have beaten me these three times (shalosh regalim)?" So we have an exact parallel with the verse in Shmot where we are commanded to have a feast "three times". (Milgrom in JPS Numbers quotes a source that perhaps the expression always used the number three.)
Since regel - foot - is a very basic word in a language, it is not surprising that a number of other meanings derive from it.
For example, the verb רגל means "to slander" or "to spy", just as a spy - a meragel מרגל - walks about on foot. A related verb is רכל - which means "to go about from place to place (for trade or gossip.)" From here we get the word markolet מרכולת - but not makolet מכולת .
Another meaning of רגל is "to be accustomed to, to be used to". Klein explains this as originally meaning "to go on foot", and from there "to go about frequently". From this meaning we get:
- הרגיל - to train, to make familiar
- התרגל - to become accustomed to
- תרגל - originally meaning "to teach to walk" in Hosea 11:3, now means "to train, to drill"
- רגיל - ragil - usual, common, customary, and also experienced, trained (as in the prayer before Mussaf on Rosh Hashana and Yom Kippur - כתפילת זקן ורגיל - "the prayers of an experienced elder".