riskant
risky
Associated with a risk; daring, dangerous, or with an uncertain outcome.
Bei diesem Wetter ist eine Bergtour eine riskante Unternehmung.
In this weather, a mountain tour is a risky undertaking.

risky
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risky
Associated with a risk; daring, dangerous, or with an uncertain outcome.
Bei diesem Wetter ist eine Bergtour eine riskante Unternehmung.
In this weather, a mountain tour is a risky undertaking.

The adjective 'riskant' (risky) is directly related to the noun 'das Risiko' (risk). If you know the noun, you can easily work out the meaning of 'riskant' (risky).
Eine Investition in diese neue Firma ist mit einem hohen Risiko verbunden, sie ist also sehr riskant.
An investment in this new company involves a high risk, so it is very risky.
A very typical sentence structure with 'riskant' (risky) is 'Es ist riskant, etwas zu tun' (It is risky to do something). This describes exactly which action is associated with a risk.
Es ist riskant, bei diesem Nebel ohne Licht zu fahren.
It is risky to drive without lights in this fog.
'Riskant' (risky) often describes abstract things like plans, decisions, or deals. Typical combinations are 'eine riskante Entscheidung' (a risky decision), 'ein riskantes Manöver' (a risky maneuver), or 'ein riskantes Geschäft' (a risky deal).
Der Chef hat eine riskante Entscheidung getroffen, die die Firma viel Geld kosten könnte.
The boss made a risky decision that could cost the company a lot of money.
sure / safe
'sicher' and 'riskant' are opposites here. 'sicher' means that something is protected from danger or harm, or does not involve much risk. 'riskant' means that something can be dangerous or has an uncertain outcome. Use 'sicher' when an action or situation seems well protected and reliable. 'riskant' fits when something can go wrong and you should be careful.

Ohne Leiter auf den Stuhl zu steigen, ist beim Streichen riskant.
Standing on a chair without a ladder is risky when painting.
Zum sicheren Arbeiten trägt er am Abend Handschuhe.
For safe work, he wears gloves in the evening.