The Collaborative International Dictionary of English v.0.48:

Minimal \Min"i*mal\, a.
   Of, pertaining to, or having a character of, a minim or
   minimum; least; smallest; as, a minimal amount or value.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

minimal
    adj 1: the least possible; "needed to enforce minimal
           standards"; "her grades were minimal"; "minimum wage"; "a
           minimal charge for the service" [syn: minimal,
           minimum] [ant: maximal, maximum]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "minimal":
   adequate, ample, baby, baby-sized, bantam, banty,
   barely sufficient, basal, basic, commensurate, compact, competent,
   corresponding, decent, diminutive, due, duodecimo, enough,
   equal to, essential, few, fit, fundamental, good, good enough,
   handy, least, littlest, lowest, miniature, miniaturized, minikin,
   minim, minimum, minuscule, nominal, plenty, plenty good enough,
   pocket, pocket-sized, pony, proportionate, satisfactory, shortest,
   slightest, small-scale, smallest, subminiature, substantial,
   sufficient, sufficient for, sufficing, suitable, tiniest, token,
   toy, twelvemo, up to, vest-pocket