Sparingly (adv) - In a manner where you only do something in spares— i.e. in small numbers/frequency.
Ex- if you have spare tires then you have extra. If you use the tires sparingly you’re trying to spare the tires—so you’re trying not to use it; you are sparing it. Use it only if you have to!
Use it in a sentence: Eating candy is usually bad for you, so eat it sparingly.