I think there's a word or an adjective for it, but I don't remember what it was. I don't want to say plan B, because that's too informal, but I remember there was a good word for it. I just don't remember it anymore.

For example:

The army was flanked by the enemies unexpectedly so that the general had to rely on his ___ plan.

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    As a footnote, I found Plan B listed in four dictionaries, and none of them listed it as informal, colloquial, or slang. (There’s nothing wrong with asking for synonyms, but it may not be as informal as you seem to think it is.)
    – J.R.
    Commented Apr 13, 2019 at 20:02
  • FWIW, I think "backup plan" is more commonplace (at least here in the US) than "fallback plan". Both are acceptable and likely as easily understood by native English speakers pretty much anywhere, but I figured it was worth noting that backup plan seems to be more common. This Google Ngram shows first usage of "backup" in 1958 vs "fallback" in 1964, with backup being ~10x more popular.
    – Doktor J
    Commented Apr 16, 2019 at 16:12

5 Answers 5


The Oxford Dictionary has


1 An alternative plan that may be used in an emergency.

Make sure you have a fallback plan in case something goes terribly wrong

So the sentence can be

The army was flanked by the enemies unexpectedly so that the general had to rely on his fallback plan.

In the context, this is particularly apt.

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    "Backup" is one I hear used a lot as well, i.e. "Luckily, he had a backup plan."
    – user34154
    Commented Apr 14, 2019 at 1:39
  • 3
    Sorry, but 'fallback' is a bad choice for this example, since it implies that it involves a retreat of some sort, which is inappropriate at best.
    – MikeB
    Commented Apr 15, 2019 at 14:08
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    @MikeBrockington You mean, because it sounds like "fall back", its meaning is the same? I disagree.
    – Mr Lister
    Commented Apr 15, 2019 at 15:44
  • 1
    Sometimes "backup" isn't an emergency plan at all but part of the main plan, that is, support. Commented Apr 15, 2019 at 17:07
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    As a native speaker in the US, this may be a valid word to use but it's rarely used. A backup plan is MUCH more common.
    – JeffC
    Commented Apr 15, 2019 at 22:21

That's often called a backup plan:

He was used as a backup plan when the remaining members of the gang failed to accomplish their mission.

This usage is also mentioned in Merriam-Webster's definition for backup:

1 a: one that serves as a substitute or support
// I brought an extra pencil for backup.
// a backup plan

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    I don't think backup plan is the most used term. Commented Apr 14, 2019 at 9:04
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    That surprises me, but check this graph. It only runs to 2008, and the growth of 'backup plan' might have been halted, but I'm really curious what the frequency nowadays is.
    – Glorfindel
    Commented Apr 14, 2019 at 13:02
  • 1
    I think the term "backup" gained a lot more technical meaning and it simply sounds like something a server administrator does.
    – Nelson
    Commented Apr 15, 2019 at 4:25
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    @DoctorPenguin yeah I have never heard anyone say "fallback" plan but loads having a backup plan.
    – WendyG
    Commented Apr 15, 2019 at 11:11
  • 1
    Yes, backup plan is the most common in American English: english-corpora.org/coca/?c=coca&q=74949944
    – user230
    Commented Apr 16, 2019 at 5:10

That could also be called a contingency or a contingency plan. The Oxford Living Dictionaries gives sense 1.1 under noun as :

A provision for a possible event or circumstance.

"stores were kept as a contingency against a blockade"

The process of developing one or several alternate plans is often called contingency planning.

Dictionary.com gives as an example:

Turkey has cooperated at times with Israel and the West on contingency planning for Syria during its civil war. (Israel Bombs Gaza While Hamas’ Kidnapping Mastermind Sits in Turkey|Eli Lake|July 1, 2014|DAILY BEAST)


For military purposes, it's Contingency Plan. This is the accepted term as taught in all leadership and mission planning courses, from Basic training to NCO Academy. The terms 'Backup Plan' and 'Fallback Plan' are NEVER used, since they have a negative connotation much in the same vein as 'Retreat'.

  • 2
    Great answer, especially since the Q has a military example.
    – Xen2050
    Commented Apr 15, 2019 at 1:05
  • As do "Abort" and "Surrender". But consider also "Auftragstaktik" borrowed from the German. Only used in very educated circles.
    – mckenzm
    Commented Apr 15, 2019 at 5:29
  • 5
    Not just a negative connotation but also could lead to misunderstandings or ambiguity. "Fallback!" is a pretty clear order to do a pretty clear thing - you don't want a commander telling people to go to the "fallback" plan and have people start running away because they misheard the context. Same reason air traffic control never use the word "takeoff" unless they are telling someone they are clear for takeoff - you don't want someone hearing the word and thinking they've been told to do something they've not.
    – J...
    Commented Apr 15, 2019 at 14:19

Informally, it can also be called a Plan B. In this case, you would say:

The army was flanked by the enemies unexpectedly so that the general had to rely on his plan B.

However, it is unlikely that military officials would use this term.

Google Dictionary defines "Plan B" as:

an alternative strategy

Which seems like what you're asking for. Plan B is used more than things like Backup Plan when speaking generally or informally, though Contingency Plan is the most applicable for the military situation.

  • The author has said explicitly in the question that "plan B" is too informal.
    – ColleenV
    Commented May 4, 2020 at 17:28

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