The Collaborative International Dictionary of English v.0.48:

Guardianship \Guard"i*an*ship\, n.
   The office, duty, or care, of a guardian; protection; care;
   watch.
   [1913 Webster]

WordNet (r) 3.0 (2006):

guardianship
    n 1: attention and management implying responsibility for
         safety; "he is in the care of a bodyguard" [syn: care,
         charge, tutelage, guardianship]
    2: the responsibility of a guardian or keeper; "he left his car
       in my keeping" [syn: guardianship, keeping,
       safekeeping]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "guardianship":
   administration, auspices, captainship, care, chairmanship, charge,
   cold storage, conservation, convenership, cure, custodianship,
   custody, dead storage, dictatorship, directorate, directorship,
   dry storage, eagle eye, foremanship, generalship, governance,
   government, governorship, guard, guardedness, guidance, handling,
   hands, headship, intendancy, invigilation, jurisdiction, keeping,
   leadership, lookout, management, managership, mastership,
   means of dealing, ministry, monitoring, observance, overseership,
   oversight, pastorage, pastorate, pastorship, patronage, peeled eye,
   preservation, presidency, proctoring, proctorship, protectorship,
   prudence, qui vive, safe hands, safekeeping, sharp eye, shelf-room,
   sovereignty, stewardship, storage, storage space, stowage,
   superintendence, superintendency, supervisorship, surveillance,
   treatment, trust, tutelage, usage, vigil, vigilance, ward,
   wardenship, wardship, warehousing, wariness, watch, watch and ward,
   watchful eye, watchfulness, watching, weather eye, wing



Bouvier's Law Dictionary, Revised 6th Ed (1856):

GUARDIANSHIP, persons. The power or protective authority given by law, and
imposed on an individual who is free and in the enjoyment of his rights,
over one whose weakness on account of his age, renders him unable to protect
himself. Vide Tutor.