caber
Caber means 'to fit inside'. It's irregular, little-used by learners, and has several idioms with a surprising reach.
caber (fit)
To fit inside something — physical or abstract space.
No cabe más gente.
There's no more room for people.
Irregular: quepo, cabes, cabe. Present only.
¿Cabemos todos en el coche?
Can we all fit in the car?
A natural question. Caber en = to fit in.
Esta mesa no cabe por la puerta.
This table won't fit through the door.
Por for movement through.
caber (idioms)
Abstract use: possible, appropriate, or conceivable.
No cabe duda.
There's no doubt.
A frequent expression. No cabe duda de que + indicative.
No me cabe en la cabeza.
I can't get my head around it.
Used for things you can't accept or understand.
Cabe destacar que...
It's worth pointing out that...
Formal writing. Cabe + infinitive = it's possible or fitting to.
Tricky bit
'Quepo' (I fit) is one of the strangest first-person forms in Spanish, and subjunctive is 'quepa'. Nobody expects learners to master it, but 'no cabe duda' is worth memorising.