An adjunct account increases the valuation of a liability account. In essence, the credit balance in this account is added to the liability account with which it is paired. The most common example of an adjunct account is the unamortized bond premium account, which is used when a business sells bonds at a premium. The unamortized bond premium and the bond liability, when combined, represent the actual liability of the bond issuer.
This concept is the reverse of a contra account, which reduces the balance of the account with which it is paired.