You will encounter "ouder" in the meaning of "parent" (see 1.) or as the comparative degree of "oud" (see 2.)

1. parent

[noun]
[de ou-der, de ou-ders]

Examples:
– "Haar moeder is een alleenstaande ouder." 
("Her mother is a single parent.")

– "Beide ouders dienen bij het gesprek aanwezig te zijn." 
("Both parents are required to be present during the consult.")

– "Zij is een kind van gescheiden ouders." 
("She is a child of divorced parents.")

– "De ouders van je ouders worden ‘grootouders’ genoemd." 
("The parents of your parents are called ‘grand parents’.")

Expressions:
– "Aanstaande ouders": expectant parents.

Example:
– "De aanstaande ouders begonnen al aardig zenuwachtig te worden."
("The expectant parents were starting to get pretty nervous." Note the use of "aardig": it can mean both "nice/friendly" or "quite/pretty".)

Related words:
– Kind: child [noun] [het kind, de kinderen].
– Ouderschap: parenthood [noun] [het ouderschap, <no plural>].

Example:
– "Ik neem al mijn ouderschapsverlof op"
("I’m taking all my parental leave." Note that maternity leave is something different: "zwangerschapsverlof".)

2. older
[comparative degree of "oud"]
[ou-der]

"Ouder" is also the comparative degree of the adjective "oud": old. A related noun derived from "ouder" is "oudere", but you will in fact only encounter it in its plural form "ouderen": elderly people.

Examples:
– "Ik ben ouder dan mijn zusje, maar ik ben niet de oudste." 
("I’m older than my (baby) sister, but I am not the oldest.")

– "Ik had mijn nicht al een tijd niet meer gezien; zij ziet er nu echt een stuk ouder uit!" 
("I hadn’t seen my cousin for quite some time; she really looks a lot older now!" Note that there a different words in Dutch for male or female cousins: "neef" and "nicht". A common mistake Dutch people make is to talk about their nephew or niece instead; this is because these are also called "neef" and "nicht" in Dutch. And while I am on the topic, note that "nicht" is also slang for a homosexual.)

Related words:
– Ouderdom: old age [noun] [de ouderdom, <no plural>].
– Ouderen: elderly people [noun, plural] [de ouderen].

Example:
– "Georganiseerde busreizen zijn populair bij ouderen."
("Organized bus tours are popular with elderly people / senior citizens.")

to get used to, to grow accustomed to, to acclimatize  
[verb]
[wen-de, ge-wend]

"Wennen" is related to getting used to something new, e.g. new
surroundings, new people, a new job. "Wennen" is usually followed by
the preposition "aan" (getting used to something). Don’t mix it up with "wenden" (wendde, gewend), which means "to turn".

Examples:
– "Ik kan maar niet wennen aan het weer in Nederland; het lijkt zes maanden per jaar te miezeren." 
("I just can’t get used to the weather in the Netherlands; it seems to drizzle for six months a year.")

– "Zij is het gewend om ‘s ochtends koffie te drinken; zonder koffie heeft ze een enorm ochtendhumeur."  ("It’s her habit to drink coffee in the morning; without coffee she is in a very bad morning mood.")

– "En, ben je al een beetje gewend aan je nieuwe baan?" 

("So, have you grown accustomed to your new job yet?")

– "Het is wel even wennen dat je nu geen auto meer hebt en het openbaar vervoer moet nemen, niet?"
-"Ach, alles went".
("It
must be quite a change now that you no longer have a car and have to
use public transport, isn’t it?" – "Well, you can get used to
everything.")

Expressions:
– "Alles went behalve een vent": you can get used to anything except for a man.

Related words:
– Wenden: to turn [verb] [wendde, gewend].
– Zich wenden tot: to turn to (someone, something) [verb] [wendde, gewend].