Un-cancellable

verb (used with object), canceled, canceling or (especially British) cancelled, cancelling.
1.
to make void; revoke; annul:
to cancel a reservation.
2.
to decide or announce that a planned event will not take place; call off:
to cancel a meeting.
3.
to mark or perforate (a postage stamp, admission ticket, etc.) so as to render invalid for reuse.
4.
to neutralize; counterbalance; compensate for:
His sincere apology canceled his sarcastic remark.
5.
Accounting.

to close (an account) by crediting or paying all outstanding charges:
He plans to cancel his account at the department store.
to eliminate or offset (a debit, credit, etc.) with an entry for an equal amount on the opposite side of a ledger, as when a payment is received on a debt.

6.
Mathematics. to eliminate by striking out a factor common to both the denominator and numerator of a fraction, equivalent terms on opposite sides of an equation, etc.
7.
to cross out (words, letters, etc.) by drawing a line over the item.
8.
Printing. to omit.
verb (used without object), canceled, canceling or (especially British) cancelled, cancelling.
9.
to counterbalance or compensate for one another; become neutralized (often followed by out):
The pros and cons cancel out.
10.
Mathematics. (of factors common to both the denominator and numerator of a fraction, certain terms on opposite sides of an equation, etc.) to be equivalent; to allow cancellation.
noun
11.
an act of canceling.
12.
Printing, Bookbinding.

omission.
a replacement for an omitted part.

verb (mainly transitive) -cels, -celling, -celled (US) -cels, -celing, -celed
1.
to order (something already arranged, such as a meeting or event) to be postponed indefinitely; call off
2.
to revoke or annul: the order for the new television set was cancelled
3.
to delete (writing, numbers, etc); cross out: he cancelled his name and substituted hers
4.
to mark (a cheque, postage stamp, ticket, etc) with an official stamp or by a perforation to prevent further use
5.
(also intransitive) usually foll by out. to counterbalance; make up for (a deficiency, etc): his generosity cancelled out his past unkindness
6.

to close (an account) by discharging any outstanding debts
(sometimes foll by out) (accounting) to eliminate (a debit or credit) by making an offsetting entry on the opposite side of the account

7.
(maths)

to eliminate (numbers, quantities, or terms) as common factors from both the numerator and denominator of a fraction or as equal terms from opposite sides of an equation
(intransitive) to be able to be eliminated in this way

noun
8.
a new leaf or section of a book replacing a defective one, one containing errors, or one that has been omitted
9.
a less common word for cancellation
10.
(music) a US word for natural (sense 20)