Ekāgratā (एकाग्रता)
ekāgratā, [-tā] f. phil. Perfect mental concentration needed for fixing the mind [dharana] in yoga.—Heritage Dictionary of Sanskrit (Dictionnaire Héritage du Sanscrit) (translated from the French)
Ekagrata, one-pointed; the perfect concentration of contemplation. (eka, one; agrata, pointed.)—Working Glossary (WQJ)
Ekagrata or Ekagratva (Occult Glossary)
Ekagrata or Ekagratva (Encyclopedic Theosophical Glossary)
Ekagrata (Wikipedia)
Ekagrata (Wiktionary [incl. etymology])
See the Yoga Sutras of Patanjali, 3:12