WordWeb Online

1. Involving two persons; intimately private
   "a head-to-head conversation";
   - tête-à-tête
    
2. Inconclusive as to outcome; close or just even in a race or comparison or competition
   "as they approached the finish line they were head-to-head";
   - neck and neck, nip and tuck [informal]

1. Even or close in a race or competition or comparison
   "the horses ran head-to-head";
   - neck and neck, nip and tuck [N. Amer, informal]

See also: inconclusive, private