What is another word for lateness?

Here are some words you could use instead of "lateness", depending on the context:

Formal:

* Tardiness

* Unpunctuality

* Delinquency (when referring to a deadline)

* Procrastination (when referring to a delay caused by putting something off)

Informal:

* Being late

* Running behind

* Coming in late

* Being delayed

* Holding up

More specific:

* Exceeding the deadline

* Missing the deadline

* Being late for work/school/the meeting

* Arriving after the scheduled time

The best word to use will depend on the specific situation and the desired tone.