The Spanish word 'manda' meaning 'vow' or 'promise' has an interesting etymology that traces back to Latin. It comes from the Latin verb 'mandare' meaning 'to entrust' or 'command', which itself is a combination of two Latin words: 'manus' meaning 'hand' and 'dare' meaning 'to give'. The literal sense was 'to put into someone's hands' or 'to entrust', which evolved into the meaning of giving a command or making a promise.

The word entered Spanish as the verb 'mandar' meaning 'to command', and from this verb came the noun 'manda' which specifically refers to a vow or promise - something that is entrusted or commanded to be done.

Some common related Spanish words include the verb 'mandar' (to command, to send), which is more frequently used than 'manda'. You might also recognize it in 'mandamiento' (commandment) and 'mandato' (mandate). All these words share the core idea of giving commands or making binding statements.

English speakers might recognize this root in words like 'mandate', 'mandatory', and 'command', all of which come from the same Latin source 'mandare'. The connection between 'hand' and command is preserved in English expressions like 'handling a situation' or 'taking matters into one's own hands'.