insuffisant

C'est insuffisant.

This is insufficient.

Le duvet des jeunes pingouins est encore insuffisant pour les garder au chaud.

The down of young penguins is still poor at keeping them warm.

C'est simplement insuffisant.

It's just not enough.

Ce que tu as fait est insuffisant.

What you did wasn't good enough.

Leur service client est gravement insuffisant.

Their customer service is severely wanting.