past- / Indo-European roots
a. fast1; shamefaced, steadfast from Old English fæst, fixed, firm;
b. avast from Middle Dutch vast, firm, fast. Both a and b from Germanic *fastuz, firm, fast.
2. fasten from Old English fæstnian, to fasten, establish, from Germanic *fastinōn, to make firm or fast.
3. handfast from Old Norse festa, to fix, affirm, from Germanic causative *fastjan, to make firm.
a. fast2 from Old English fæstan, to abstain from food;
b. breakfast from Old Norse fasta, to abstain from food. Both a and b from Germanic *fastēn, to hold fast, observe abstinence.
[Pokorny pasto- 789.]