fall back

Short definition from Wiktionary

Verb

1. 1
   Used other than figuratively or idiomatically: see fall, back.
2. 2
   To retreat.
3. 3
   To fail to fulfill a promise or purpose.
4. 4
   To turn the clocks back for the end of daylight saving time.

Noun

1. 1
   Alternative form of fallback.