The chemical compound that has been used up in the reaction between sodium hydroxide and hydrochloric acid (HCl) is sodium hydroxide (NaOH).

When sodium hydroxide (NaOH) and hydrochloric acid (HCl) react, they undergo a neutralization reaction, which results in the formation of sodium chloride (NaCl) and water (H2O). The reaction can be represented as follows:

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

In this reaction, sodium hydroxide and hydrochloric acid are both consumed or used up, and the products formed are sodium chloride and water.