Gebrechlich means 'frail' or 'fragile'. It's a poignant word often used to describe something delicate and easily broken, like an elderly person's health.
In the song, Apache 207 sings, "Um uns alles gebrechlich" (Around us, everything is fragile). He uses this powerful adjective to describe the delicate state of their relationship before his grand gesture of returning with a new boat. This word beautifully captures the vulnerability and tension of the moment, making it incredibly memorable.
This song is one big, brilliant metaphor. Apache 207 is talking to an ex who left him back when he didn't have much to offer. He remembers her leaving because his life, his 'boat', just wasn't good enough for her ambitions. He describes it as having only tiny paddles, “Die Paddel waren so klein hier” (The paddles were so small here), and no motor. She thought his sail was too small and “Das Meer war dir zu stürmisch” (The sea was too stormy for you).
But things have changed. The whole chorus is a flex. He's telling her he's coming back for her, but this time with a new boat ready for the “offene Meer” (open sea). He makes it very clear that the past is the past and his situation is different now: “Doch das alte Boot gibt es nicht mehr” (But the old boat doesn't exist anymore). It’s a classic story of someone making it big and going back to the person who didn't believe in them.