The Collaborative International Dictionary of English v.0.48:

Diagnose \Di`ag*nose"\, v. t. & i.
   To ascertain by diagnosis; to diagnosticate. See
   Diagnosticate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

diagnose
    v 1: determine or distinguish the nature of a problem or an
         illness through a diagnostic analysis [syn: diagnose,
         name]
    2: subject to a medical analysis

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "diagnose":
   bandage, bathe, care for, construe, cure, define, describe,
   determinate, determine, distinguish, doctor, finger, flux,
   give care to, heal, identify, interpret, massage, minister to,
   name, nurse, operate on, physic, pinpoint, place, plaster,
   poultice, purge, read, read into, recognize, remedy, rub, splint,
   spot, strap, take, take it that, take to mean, treat, understand,
   understand by