Reasoning
This is the only word that cannot be spelled using a calculator.
For example, if you enter 376616 into an old-fashioned calculator, and look at the number upside down, you can read GIGGLE.
376616 = giggle
7105 = soil
57738 = bells
378806 = gobble
4506 = gosh
5508 = boss
3704 = hole
5355378 = blesses
coil = N/A