The most common and most likely answer to this crossword clue is the 3 letter word FIG
I've seen this crossword clue in The Times
F
I
G
More clues leading to the result FIG
Buddy explains!

The straight part
We know that "amount that can be ignored?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case amount that can be ignored? = fig.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 FIG mean?
FIG noun- A fruit-bearing tree or shrub of the genus Ficus that is native mainly to the tropics.
- The fruit of the fig tree, pear-shaped and containing many small seeds.
- A small piece of tobacco.
- The value of a fig, practically nothing; a fico; a whit.
- A raisin (dried grape)
- To insult with a fico, or contemptuous motion.
- To put into the head of, as something useless or contemptible.
- (soap-making) To develop, or cause (a soap) to develop, white streaks or granulations.
- To move suddenly or quickly; rove about.
- A person's figure; dress or appearance.
- To dress; to get oneself up a certain way.
- A drawing or diagram conveying information.
- The representation of any form, as by drawing, painting, modelling, carving, embroidering, etc.; especially, a representation of the human body.
- A person or thing representing a certain consciousness.
- The appearance or impression made by the conduct or career of a person.
- Distinguished appearance; magnificence; conspicuous representation; splendour; show.
- A human figure, which dress or corset must fit to; the shape of a human body.
- A numeral.
- A number, an amount.
- A shape.
- A visible pattern as in wood or cloth.
- Any complex dance moveW.
- A figure of speech.
- The form of a syllogism with respect to the relative position of the middle term.
- A horoscope; the diagram of the aspects of the astrological houses.
- Any short succession of notes, either as melody or as a group of chords, which produce a single complete and distinct impression.
- A form of melody or accompaniment kept up through a strain or passage; a motif; a florid embellishment.
- To insert a ginger root into the anus, vagina or urethra of: to perform figging upon.