[tbw2]

Dany is Jon’s half aunt.

[ConjunctionJunction]

Dany is Jon's aunt (full aunt). Rhaegar and Dany share the same parents (Mad King Aerys and Queen Rhaella), so Rhaegar and Dany are full brother and sister.

If Rhaegar and Dany only shared one parent, then Dany could be said to be Jon's half aunt.