My silly mnemonic: You use your nose-a to nusa.
Haha, I love it!
And Nasya is an Ayurvedic treatment for noses, e.g. if you have the sniffles.
Should "to smell" be accepted, or is this a more specific form?
My guess is they use "to sniff" to differentiate from "to smell" meaning to be smelly.
kunusa - to smell, to sniff
To sniff also in the meaning of taking (sniffing) drugs?
To smell ....is a fine answer