zwecklos
pointless
Describes an action or attempt that cannot have a goal or success and is therefore pointless.
Jeder Versuch, ihn vom Gegenteil zu überzeugen, war zwecklos.
Every attempt to convince him otherwise was pointless.

pointless
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pointless
Describes an action or attempt that cannot have a goal or success and is therefore pointless.
Jeder Versuch, ihn vom Gegenteil zu überzeugen, war zwecklos.
Every attempt to convince him otherwise was pointless.

The word is made up of the noun 'der Zweck' (purpose, aim) and the ending '-los' (without). So 'zwecklos' literally means 'without a purpose' or 'without sense'.
Ohne den richtigen Schlüssel ist jeder Versuch, die Tür zu öffnen, zwecklos.
Without the right key, every attempt to open the door is pointless.
A very common construction is 'Es ist zwecklos, etwas zu tun' (It is pointless to do something). After the comma comes an infinitive clause with 'zu'.
Es ist zwecklos, bei diesem Regen auf den Bus zu warten.
It is pointless to wait for the bus in this rain.
'Zwecklos' often describes actions or efforts. Typical combinations are 'ein zweckloser Versuch' (a pointless attempt), 'eine zwecklose Debatte' (a pointless debate), or the well-known phrase 'Widerstand ist zwecklos' (Resistance is futile).
Nach einer Stunde gaben wir die zwecklose Suche auf.
After an hour, we gave up the pointless search.
sensible
'sinnvoll' and 'zwecklos' are opposites, but 'zwecklos' is a little narrower. 'sinnvoll' says that something has a benefit or a good purpose. 'zwecklos' says that an attempt or action cannot reach a goal and therefore achieves nothing. Especially with efforts, discussions, or requests, 'zwecklos' fits when you mean: it will not succeed anyway.

Es ist zwecklos, weiter zu warten, weil der Zug heute nicht mehr fährt.
It is pointless to keep waiting because the train is not running anymore today.
Bei der Bewerbung ist ein kurzes Gespräch mit einem Freund oft sinnvoll.
When applying for a job, a short conversation with a friend is often sensible.