Bridge placed over key area supplying basic condiment (7)

'basic condiment' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'bridge placed over key area' is the wordplay.
I cannot really understand how this works, but
'key' could be 'alt' (the Alt keyboard button) and 'alt' is located in the answer.
'bridge' could be 'span' (synonyms) and 'span' is located in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

'supplying' acts as a link.

Can you help me to learn more?