1. ash, ashes
[noun]

[de as, de as-sen]

The grayish-white to black powdery residue left when something
is burned, is called "as". "As" has no plural form, so both ash and ashes translate to "as".

Examples:
– "Pas op met die peuk, de as valt op de vloerbedekking." 
("Watch out with that cigarette, the ash is dropping on the carpet.")

– "De vulkaan in IJsland heeft een enorme wolk van as de dampkring ingestoten." 
("The Iceland volcano has thrust a huge cloud of ash into the atmosphere.")

Expressions:
–
"In de as leggen": (lit.: to lay in the ash) to reduce to ashes.

Related words:
– Peuk: smoke, fag, cig(arette) [noun] [de peuk, de peuken].
– Asbak: ash tray [noun] [de asbak, de asbakken].

Example:
– "Schat
heb je weer gerookt? Je ruikt naar asbak…"
("Baby have you been
smoking again? You smell like an ashtray…") 

– Assepoester: Cinderella [noun] [de Assepoester, de Assepoesters], see Extra.

Extra:
In Dutch, Cinderella is called Assepoester. She’s called "assepoester" because – forced by the wicked stepmother and her daughters – she’s had to do a lot of dirty shores, such as lighting the fireplace, which made her have a lot of ash stains on her face and clothes. "Poester" is probably derived from or a corruption of "poetsen": to clean. So literally "Assepoester" would be "ash cleaning woman"…

2. axis
[noun]
[de as, de as-sen]

An "as" is also an axis. In this case, "as" has a plural form: "assen".

Examples:
– "De as van het kwaad bestaat uit een aantal schurkenstaten." 
("The axis of evil consists of a number of rogue states.")

– "De aarde draait in 24 uur om zijn as." 
("The earth revolves on its axis in 24 hours.")

– "Tijd staat op de x-as, winst op de y-as." 
("Time is on the x-axis, profit on the y-axis.")

Related words:
– Spil: pivot [noun] [de spil, de spillen].

3. A flat
[noun]
[de as, de as-sen]

"As" is also a musical note or key.

Examples:
– "Chopins wals in As Groot is niet erg makkelijk om te spelen." 
("Chopin’s waltz in A-flat major is not very easy to play.")

– "Chopin stond erom bekend dat hij veel stukken in as groot componeerde."
("Chopin was known for composing a lot of pieces in A-flat major.")

Expressions:
–
"Een gevoelig snaar raken": to touch (upon) a tender string, to strike a sensitive chord.

Example:
– "Heb je hem al gevraagd of hij wil trouwen?"
– "Nee, dat raakt een gevoelige snaar…"
("Have you already asked him if he wants to get
married?" – "No, that touches upon a tender string…") 

Related words:
– Toonladder: scale [noun] [de toonladder, de toonladders].
– Noot: note, key [noun] [de noot, de noten].
– La: <musical note> la [noun] [de la, de la’s].

Example:
– "Do – re – mi – fa – sol – la – si – do!"
("Do – re – mi – fa – sol
– la – ti – do!" Note that the "si" is not a typo!)