strictly

adverb4

1. •
   firmly, in a way that lets nobody break the rules

   • He adhered strictly to the diet his doctor prescribed.
2. •
   In a limited manner; only

   • This work was strictly voluntary, but any animal who absented himself from it would have his rations reduced by half. — 1943
3. •
   In a narrow or limited sense.

   • That term refers strictly to smaller birds.
4. •
   In a manner that applies to every member of a set or every interval of a function