ti‘avā, in the phrase toka ti‘avā. Cornerstone, keystone.

Ka anoano ma‘ata‘ia te toka ti‘avā e te aronga patu ‘are nō te ‘ākoko o te ‘are.
The housebuilders badly need a main cornerstone for the corner of the house;

‘E toka ti‘avā tei tuku‘ia ki runga ake i te ngūtupa ‘ei tango.
The keystone was wedged over the door as a support.