Warehou means: Any of the three medusafishes: (the common warehou), (the white warehou), and (the silver warehou).. It is mainly New Zealand English and may not be understood outside that context. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.