Crossword Genius

It's in our blood (5)

Ross

I believe the answer is:

serum

I'm a little stuck... Click here to teach me more about this clue!

'blood' is the definition.
(thesaurus)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for serum that I've seen before include "Part of blood; vaccine" , "potential shot in the arm?" , "Antidote" , "Constituent of blood" , "Antitoxin derived from blood" .)

I've seen this clue in The Globe and Mail.
Want a hint initially instead of a full solution? Install my app