Here are the entries for upāsanā and aupāsana from āpte's and monier william's sanskrit-english dictionaries.

āpṭe

उपासनम् ना 

  • -1 Service, serving, attendance, waiting upon; 
    • शीलं खलोपासनात् (विनश्यति); 
    • उपासनामेत्य पितुः स्म सृज्यते N.1.34; 
    • Pt.1.169; Ms.3.17; Bg.13.7; Y.3.156; Bh.2.42. 
  • -2 Engaging in, being intent on, performing; 
    • संगीत˚ Mk.6; सन्ध्या˚ Ms.2.69. 
  • -3 Worship, respect, adoration. 
  • -4 Practice of archery. 
  • -5 Regarding as, reflecting upon. 
  • -6 Religious meditation. 
    • न कर्मसांख्ययोगोपासनादिभिः Mukti Up.1.1. 
  • -7 The sacred fire. 
    • वानप्रस्थो ब्रह्मचारी साग्निः सोपासनो व्रजेत्. Y.3.45. 
  • -8 Injuring, hurting; (fr. अस् 2). 
  • -Comp. -उपासना- खण्डः, N. of the first section of the Gaṇeśa Purāṇa.
औपासन a. (-नी f.) [उपासन-अण्] 
  • -1 Ralating to गृह्याग्नि or household fire. 
  • -2 Belonging to worship or service; holy, sacred.
औपासनः 
  • 1 A fire used for domestic worship. 
  • -2 A small rice-ball (पिण्ड) offered to the manes.

monier williams

उपासन / उपा n. 
  • the act of throwing off (arrows) , exercise in archery MBh.
  • the act of sitting or being near or at hand
  • serving , waiting upon , service , attendance , respect A1p. Gaut. Mn. Ya1jn5. etc.
  • homage , adoration , worship (with रामानुज s , consisting of five parts , viz. अभिगमन or approach , उपादान or preparation of offering , इज्या or oblation , स्वाध्याय or recitation , and योग or devotion) Sarvad. Veda1ntas. etc.
  • a seat Vait.
  • the being intent on or engaged in Mr2icch. R.
  • domestic fire Ya1jn5. iii , 45.
औपासन m. 
  • ( scil. अग्नि ) , (fr. उपा-सन ) , the fire used for domestic worship S3Br. xii Ka1tyS3r. Pa1rGr2. etc. 
  • ( scil. पिण्ड ) a small cake offered to the Manes S3a1n3khBr. and S3a1n3khS3r.
औपासन 
  • mf( आ )n. relating to or performed at an औपासन fire (as the evening and morning oblations) Ya1jn5. iii,17 HirGr2.