The answer is APACE (5 letters).
Why APACE fits
APACE is the crossword standard for very quickly. It is an archaic adverb meaning at a quick pace, and it survives almost entirely in puzzles and in the phrase continuing apace. Five letters with three vowels is exactly the shape constructors reach for.
Every answer by letter count
| Letters | Answer | When it is used |
|---|---|---|
| 5 | APACE | The default for this clue |
| 6 | PRONTO | Informal register, from Spanish |
| 4 | FAST | Plain adverb, short slots |
| 6 | INAJIF | As in in a jiffy, rendered without spaces |
| 7 | INAFLASH | Longer slots, phrase answer |
| 6 | PRESTO | When the clue hints at magic or music |
Clues that share these answers
- Speedily
- Without delay
- In no time
- Go quickly
- Write quickly, as a note
Register is the hidden signal
Setters choose between these answers partly on tone. APACE is literary and slightly archaic, so it turns up when the surrounding clues are formal. PRONTO is casual and borrowed from Spanish, so it appears in puzzles with a lighter register. INAFLASH and INAJIF are phrase answers and only appear when the grid has a long slot to fill.
If you are stuck, the surrounding fill often tells you which register the constructor is working in, and that narrows the choice before you have a single crossing letter.
The phrase answers worth memorising
Speed clues generate more multi-word answers than almost any other category, because English is unusually rich in idioms for it. INAFLASH, INNOTIME, ATONCE and LICKETYSPLIT all appear once a grid has room. LICKETYSPLIT is a particular constructor favourite for long slots because its letter mix is odd enough to lock the surrounding entries into place.
When a long across entry is clued for speed and you already have an initial I or L, run that list before trying to build the answer letter by letter from crossings.
Confirming it in your grid
Count the squares before committing. If the length matches the row above and one crossing letter agrees, you can fill the rest with confidence. When two answers of the same length both fit the clue, the crossings decide it, and it is usually faster to solve the crossing entry than to argue with the definition.