The most common and most likely answer to this crossword clue is the 2 letter word DE
D
E
More clues leading to the result DE
- Reduction in level of French euphoria about southern California
- One degree Celsius in river in thaw
- Tail off dace and eels cooked over half heat
- Judge quietly owns hugging spinster regularly reduces stress
- Decide to lose 500 then change to warm up
- Reduce extent of climbing plant, state overdue
- Remove cold coat from apparatus, shedding volume
- Having reduced hazards, skied freely on red run
- Decries liquid aids to making out
Buddy explains!

The straight part
We know that "Tail off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tail off = de.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DE mean?
DE verb- To do.
- A meaningless syllable used when singing a tune or indicating a rhythm.